Remove hardcoded command paths in systemd unit files

Depending on the distro, common commands like sleep and chown may either
be located in /bin or /usr/bin.

Systemd added path lookup to ExecStart in v239, allowing only the
command name to be put in unit files and not the full path as
historically required. At least Ubuntu 18.04 LTS is however still on
v237 so we should maintain portability for a while longer.

roles/matrix-synapse/templates/goofys/systemd/matrix-goofys.service.j2

@@ -6,10 +6,10 @@ Requires=docker.service
 
 [Service]
 Type=simple
-ExecStartPre=-/usr/bin/docker kill %n
-ExecStartPre=-/usr/bin/docker rm %n
+ExecStartPre=-{{ matrix_host_command_docker }} kill %n
+ExecStartPre=-{{ matrix_host_command_docker }} rm %n
 
-ExecStart=/usr/bin/docker run --rm --name %n \
+ExecStart={{ matrix_host_command_docker }} run --rm --name %n \
 			--log-driver=none \
 			--user={{ matrix_user_uid }}:{{ matrix_user_gid }} \
 			-v /etc/passwd:/etc/passwd:ro \
@@ -25,10 +25,10 @@ ExecStart=/usr/bin/docker run --rm --name %n \
 			-c 'goofys -f{% if not matrix_s3_media_store_custom_endpoint_enabled %} --storage-class=STANDARD_IA{% endif %}{% if matrix_s3_media_store_custom_endpoint_enabled %} --endpoint={{ matrix_s3_media_store_custom_endpoint }}{% endif %} --region {{ matrix_s3_media_store_region }} --stat-cache-ttl 60m0s --type-cache-ttl 60m0s --dir-mode 0700 --file-mode 0700 {{ matrix_s3_media_store_bucket_name }} /s3'
 
 TimeoutStartSec=5min
-ExecStop=-/usr/bin/docker stop %n
-ExecStop=-/usr/bin/docker kill %n
-ExecStop=-/usr/bin/docker rm %n
-ExecStop=-/bin/fusermount -u {{ matrix_synapse_media_store_path }}
+ExecStop=-{{ matrix_host_command_docker }} stop %n
+ExecStop=-{{ matrix_host_command_docker }} kill %n
+ExecStop=-{{ matrix_host_command_docker }} rm %n
+ExecStop=-{{ matrix_host_command_fusermount }} -u {{ matrix_synapse_media_store_path }}
 Restart=always
 RestartSec=5
 SyslogIdentifier=matrix-goofys