Do not report docker kill/rm attempts as errors

These are just defensive cleanup tasks that we run.
In the good case, there's nothing to kill or remove, so they trigger an
error like this:

> Error response from daemon: Cannot kill container: something: No such container: something

and:

> Error: No such container: something

People often ask us if this is a problem, so instead of always having to
answer with "no, this is to be expected", we'd rather eliminate it now
and make logs cleaner.

In the event that:
- a container is really stuck and needs cleanup using kill/rm
- and cleanup fails, and we fail to report it because of error
suppression (`2>/dev/null`)

.. we'd still get an error when launching ("container name already in use .."),
so it shouldn't be too hard to investigate.

roles/matrix-jitsi/templates/jicofo/matrix-jitsi-jicofo.service.j2

@@ -10,8 +10,8 @@ DefaultDependencies=no
 [Service]
 Type=simple
 Environment="HOME={{ matrix_systemd_unit_home_path }}"
-ExecStartPre=-{{ matrix_host_command_docker }} kill matrix-jitsi-jicofo
-ExecStartPre=-{{ matrix_host_command_docker }} rm matrix-jitsi-jicofo
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-jicofo 2>/dev/null'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-jicofo 2>/dev/null'
 
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-jicofo \
 			--log-driver=none \
@@ -23,8 +23,8 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-jicofo \
 			{% endfor %}
 			{{ matrix_jitsi_jicofo_docker_image }}
 
-ExecStop=-{{ matrix_host_command_docker }} kill matrix-jitsi-jicofo
-ExecStop=-{{ matrix_host_command_docker }} rm matrix-jitsi-jicofo
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-jicofo 2>/dev/null'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-jicofo 2>/dev/null'
 Restart=always
 RestartSec=30
 SyslogIdentifier=matrix-jitsi-jicofo

roles/matrix-jitsi/templates/jvb/matrix-jitsi-jvb.service.j2

@@ -10,8 +10,8 @@ DefaultDependencies=no
 [Service]
 Type=simple
 Environment="HOME={{ matrix_systemd_unit_home_path }}"
-ExecStartPre=-{{ matrix_host_command_docker }} kill matrix-jitsi-jvb
-ExecStartPre=-{{ matrix_host_command_docker }} rm matrix-jitsi-jvb
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-jvb 2>/dev/null'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-jvb 2>/dev/null'
 
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-jvb \
 			--log-driver=none \
@@ -32,8 +32,8 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-jvb \
 			{% endfor %}
 			{{ matrix_jitsi_jvb_docker_image }}
 
-ExecStop=-{{ matrix_host_command_docker }} kill matrix-jitsi-jvb
-ExecStop=-{{ matrix_host_command_docker }} rm matrix-jitsi-jvb
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-jvb 2>/dev/null'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-jvb 2>/dev/null'
 Restart=always
 RestartSec=30
 SyslogIdentifier=matrix-jitsi-jvb

roles/matrix-jitsi/templates/prosody/matrix-jitsi-prosody.service.j2

@@ -10,8 +10,8 @@ DefaultDependencies=no
 [Service]
 Type=simple
 Environment="HOME={{ matrix_systemd_unit_home_path }}"
-ExecStartPre=-{{ matrix_host_command_docker }} kill matrix-jitsi-prosody
-ExecStartPre=-{{ matrix_host_command_docker }} rm matrix-jitsi-prosody
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-prosody 2>/dev/null'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-prosody 2>/dev/null'
 
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-prosody \
 			--log-driver=none \
@@ -24,8 +24,8 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-prosody
 			{% endfor %}
 			{{ matrix_jitsi_prosody_docker_image }}
 
-ExecStop=-{{ matrix_host_command_docker }} kill matrix-jitsi-prosody
-ExecStop=-{{ matrix_host_command_docker }} rm matrix-jitsi-prosody
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-prosody 2>/dev/null'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-prosody 2>/dev/null'
 Restart=always
 RestartSec=30
 SyslogIdentifier=matrix-jitsi-prosody

roles/matrix-jitsi/templates/web/matrix-jitsi-web.service.j2

@@ -10,8 +10,8 @@ DefaultDependencies=no
 [Service]
 Type=simple
 Environment="HOME={{ matrix_systemd_unit_home_path }}"
-ExecStartPre=-{{ matrix_host_command_docker }} kill matrix-jitsi-web
-ExecStartPre=-{{ matrix_host_command_docker }} rm matrix-jitsi-web
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-web 2>/dev/null'
+ExecStartPre=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-web 2>/dev/null'
 
 ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-web \
 			--log-driver=none \
@@ -27,8 +27,8 @@ ExecStart={{ matrix_host_command_docker }} run --rm --name matrix-jitsi-web \
 			{% endfor %}
 			{{ matrix_jitsi_web_docker_image }}
 
-ExecStop=-{{ matrix_host_command_docker }} kill matrix-jitsi-web
-ExecStop=-{{ matrix_host_command_docker }} rm matrix-jitsi-web
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} kill matrix-jitsi-web 2>/dev/null'
+ExecStop=-{{ matrix_host_command_sh }} -c '{{ matrix_host_command_docker }} rm matrix-jitsi-web 2>/dev/null'
 Restart=always
 RestartSec=30
 SyslogIdentifier=matrix-jitsi-web