Make media-store restore work with server files, not local

This is a simplification and a way to make it consistent with
how we do Postgres imports (see 6d89319822), using
files coming from the server, not from the local machine.

By encouraging people NOT to use local files,
we potentially avoid problems such as #34 (Github issue),
where people would download `media_store` to their Mac's filesystem
and case-sensitivity issues will actually corrupt it.

By not encouraging local files usage, it's less likely that
people would copy (huge) directories to their local machine like that.

roles/matrix-server/tasks/import/import_media_store.yml

@@ -1,49 +1,54 @@
 ---
 
+# Pre-checks
+
 - name: Fail if playbook called incorrectly
-  fail: msg="The `local_path_media_store` variable needs to be provided to this playbook, via --extra-vars"
-  when: "local_path_media_store is not defined or local_path_media_store.startswith('<')"
+  fail: msg="The `server_path_media_store` variable needs to be provided to this playbook, via --extra-vars"
+  when: "server_path_media_store is not defined or server_path_media_store.startswith('<')"
+
+- name: Fail if media store is on Amazon S3
+  fail: msg="Your media store is on Amazon S3. Due to technical limitations, restoring is not supported."
+  when: "matrix_s3_media_store_enabled"
 
 - name: Check if the provided media store directory exists
-  stat: path="{{ local_path_media_store }}"
-  delegate_to: 127.0.0.1
-  become: false
-  register: local_path_media_store_stat
+  stat: path="{{ server_path_media_store }}"
+  register: server_path_media_store_stat
 
-- name: Fail if provided media store directory doesn't exist on the local machine
-  fail: msg="{{ local_path_media_store }} cannot be found on the local machine"
-  when: "not local_path_media_store_stat.stat.exists or not local_path_media_store_stat.stat.isdir"
+- name: Fail if provided media store directory doesn't exist on the server
+  fail: msg="{{ server_path_media_store }} cannot be found on the server"
+  when: "not server_path_media_store_stat.stat.exists or not server_path_media_store_stat.stat.isdir"
 
 - name: Check if media store contains local_content
-  stat: path="{{ local_path_media_store }}/local_content"
-  delegate_to: 127.0.0.1
-  become: false
-  register: local_path_media_store_local_content_stat
+  stat: path="{{ server_path_media_store }}/local_content"
+  register: server_path_media_store_local_content_stat
 
 - name: Check if media store contains remote_content
-  stat: path="{{ local_path_media_store }}/remote_content"
-  delegate_to: 127.0.0.1
-  become: false
-  register: local_path_media_store_remote_content_stat
+  stat: path="{{ server_path_media_store }}/remote_content"
+  register: server_path_media_store_remote_content_stat
 
 - name: Fail if media store directory doesn't look okay (lacking remote and local content)
-  fail: msg="{{ local_path_media_store }} contains neither local_content nor remote_content. It's most likely a mistake and is not a media store directory."
-  when: "not local_path_media_store_local_content_stat.stat.exists and not local_path_media_store_remote_content_stat.stat.exists"
+  fail: msg="{{ server_path_media_store }} contains neither local_content nor remote_content directories. It's most likely a mistake and is not a media store directory."
+  when: "not server_path_media_store_local_content_stat.stat.exists and not server_path_media_store_remote_content_stat.stat.exists"
+
+
+# Actual import work
 
 - name: Ensure matrix-synapse is stopped
   service: name=matrix-synapse state=stopped daemon_reload=yes
   register: stopping_result
 
-- name: Ensure provided media store directory is copied to the server
+# This can only work with local files, not if the media store is on Amazon S3,
+# as it won't be accessible in such a case.
+- name: Ensure provided media store directory is synchronized
   synchronize:
-    src: "{{ local_path_media_store }}/"
+    src: "{{ server_path_media_store }}/"
     dest: "{{ matrix_synapse_media_store_path }}"
     delete: yes
     # It's wasteful to preserve owner/group now. We chown below anyway.
     owner: no
     group: no
-    times: "{{ False if matrix_s3_media_store_enabled else True }}"
-    perms: "{{ False if matrix_s3_media_store_enabled else True }}"
+    times: yes
+  delegate_to: "{{ inventory_hostname }}"
 
 # This is for the generic case and fails in other cases (remote file systems),
 # because in such cases the base path (matrix_synapse_media_store_path) is a mount point.