UCA: Uncomment UCA variables in defaults, fix consequent breakage

The Ubuntu Cloud Archive-related (UCA) defaults in
roles/ceph-defaults/defaults/main.yml were commented out, which means
if you set `ceph_repository` to "uca", you get undefined variable
errors, e.g.

```
The task includes an option with an undefined variable. The error was: 'ceph_stable_repo_uca' is undefined

The error appears to have been in '/nfs/users/nfs_m/mv3/software/ceph-ansible/roles/ceph-common/tasks/installs/debian_uca_repository.yml': line 6, column 3, but may
be elsewhere in the file depending on the exact syntax problem.

The offending line appears to be:

- name: add ubuntu cloud archive repository
  ^ here

```

Unfortunately, uncommenting these results in some other breakage,
because further roles were written that use the fact of
`ceph_stable_release_uca` being defined as a proxy for "we're using
UCA", so try and install packages from the bionic-updates/queens
release, for example, which doesn't work. So there are a few `apt` tasks
that need modifying to not use `ceph_stable_release_uca` unless
`ceph_origin` is `repository` and `ceph_repository` is `uca`.

Closes: #3475
Signed-off-by: Matthew Vernon <mv3@sanger.ac.uk>

group_vars/all.yml.sample

@@ -212,7 +212,7 @@ dummy:
 #
 #ceph_stable_repo_uca: "http://ubuntu-cloud.archive.canonical.com/ubuntu"
 #ceph_stable_openstack_release_uca: queens
-#ceph_stable_release_uca: "{{ansible_lsb.codename}}-updates/{{ceph_stable_openstack_release_uca}}"
+#ceph_stable_release_uca: "{{ ansible_lsb.codename }}-updates/{{ ceph_stable_openstack_release_uca }}"
 
 # REPOSITORY: openSUSE OBS
 #

group_vars/rhcs.yml.sample

@@ -212,7 +212,7 @@ ceph_rhcs_version: 3
 #
 #ceph_stable_repo_uca: "http://ubuntu-cloud.archive.canonical.com/ubuntu"
 #ceph_stable_openstack_release_uca: queens
-#ceph_stable_release_uca: "{{ansible_lsb.codename}}-updates/{{ceph_stable_openstack_release_uca}}"
+#ceph_stable_release_uca: "{{ ansible_lsb.codename }}-updates/{{ ceph_stable_openstack_release_uca }}"
 
 # REPOSITORY: openSUSE OBS
 #

roles/ceph-common/tasks/installs/install_debian_packages.yml

@@ -4,6 +4,6 @@
     name: "{{ debian_ceph_pkgs | unique }}"
     update_cache: no
     state: "{{ (upgrade_ceph_packages|bool) | ternary('latest','present') }}"
-    default_release: "{{ ceph_stable_release_uca | default('') }}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
+    default_release: "{{ ceph_stable_release_uca | default('') if ceph_origin == 'repository' and ceph_repository == 'uca' else '' }}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
   register: result
   until: result is succeeded

roles/ceph-defaults/defaults/main.yml

@@ -202,9 +202,9 @@ ceph_rhcs_cdn_debian_repo_version: "/3-release/" # for GA, later for updates use
 # usually has newer Ceph releases than the normal distro repository.
 #
 #
-#ceph_stable_repo_uca: "http://ubuntu-cloud.archive.canonical.com/ubuntu"
-#ceph_stable_openstack_release_uca: queens
-#ceph_stable_release_uca: "{{ansible_lsb.codename}}-updates/{{ceph_stable_openstack_release_uca}}"
+ceph_stable_repo_uca: "http://ubuntu-cloud.archive.canonical.com/ubuntu"
+ceph_stable_openstack_release_uca: queens
+ceph_stable_release_uca: "{{ ansible_lsb.codename }}-updates/{{ ceph_stable_openstack_release_uca }}"
 
 # REPOSITORY: openSUSE OBS
 #

roles/ceph-mds/tasks/non_containerized.yml

@@ -3,7 +3,7 @@
   apt:
     name: ceph-mds
     state: "{{ (upgrade_ceph_packages|bool) | ternary('latest','present') }}"
-    default_release: "{{ ceph_stable_release_uca | default('') }}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
+    default_release: "{{ ceph_stable_release_uca | default('') if ceph_origin == 'repository' and ceph_repository == 'uca' else '' }}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
   when:
     - mds_group_name in group_names
     - ansible_os_family == 'Debian'

roles/ceph-mgr/tasks/pre_requisite.yml

@@ -12,7 +12,7 @@
   apt:
     name: ceph-mgr
     state: "{{ (upgrade_ceph_packages|bool) | ternary('latest','present') }}"
-    default_release: "{{ ceph_stable_release_uca | default('') }}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
+    default_release: "{{ ceph_stable_release_uca | default('') if ceph_origin == 'repository' and ceph_repository == 'uca' else ''}}{{ ansible_distribution_release ~ '-backports' if ceph_origin == 'distro' and ceph_use_distro_backports else '' }}"
   register: result
   until: result is succeeded
   when: