tests: Use ansible_pkg_mgr fact to determine the BTRFS package

The ansible_distribution variable is causing some troubles since it can
contain spaces etc. As such, we can simply use the ansible_pkg_mgr
module to figure out the name of the package we want to install.

Change-Id: Ic92eb1f9030df2883b049b9868e031ff4f0d42f2

tests/test-create-btrfs-dev.yml

@@ -22,7 +22,7 @@
     - block:
       - name: Install BTRFS packages
         package:
-          name: "{{ btrfs_package[ansible_distribution | lower] }}"
+          name: "{{ btrfs_package[ansible_pkg_mgr | lower] }}"
           state: present
 
       - name: Create base directories
@@ -55,6 +55,6 @@
         - lxc_container_backing_store == 'btrfs'
   vars:
     btrfs_package:
-      ubuntu: "btrfs-tools"
-      redhat: "btrfs-progs"
-      suse: "btrfsprogs"
+      apt: "btrfs-tools"
+      yum: "btrfs-progs"
+      zypper: "btrfsprogs"