Minor fixes for installation and custom user handling (#23)

First change introduces `restic_version` for handling file name in `/tmp/`. This will allow upgrades and downgrades of `restic` client in environments that are not constantly restarting/reloading/cleaning up (Ansible Tower in our case).

Second change enforces `restic_user` variable on the installed `restic` client. I think this actually wouldn't work should you specify any different user in the variable as there's '0750' mode on the file, which would lack the executable bit for the group (that was set properly via `restic_group`).

tasks/install.yml

@@ -31,16 +31,16 @@
 
 - name: Decompress the binary
   become: false
-  shell: "bzip2 -dc /tmp/restic_{{ restic_version }}_{{ ansible_system | lower }}_{{ go_arch_map[ansible_architecture] | default(ansible_architecture) }}.bz2 > /tmp/restic"
+  shell: "bzip2 -dc /tmp/restic_{{ restic_version }}_{{ ansible_system | lower }}_{{ go_arch_map[ansible_architecture] | default(ansible_architecture) }}.bz2 > /tmp/restic_{{ restic_version }}"
   args:
-    creates: "/tmp/restic"
+    creates: "/tmp/restic_{{ restic_version }}"
   delegate_to: localhost
   run_once: true
   check_mode: false
 
 - name: Propagate restic binary
   copy:
-    src: /tmp/restic
+    src: "/tmp/restic_{{ restic_version }}"
     dest: '{{ restic_install_path }}/restic'
     mode: '0750'
     owner: 'root'