bootstrap-host: Create swap without using a failed task

This reverts commit 541f04e546 and
implements a more targeted solution.

Unfortunately this implementation's of a try/rescue system which
will always fail the try on a fresh system causes a lot of confusion
for anyone new to OSA. When seeing the reported failed task the
user thinks something went wrong, even though it was working as
designed.

The main.yml uses a conditional include for the execution of these
tasks only if the current swap available < 1MB. This should be enough
to prevent the tasks executing again. If they do execute again, then
the task to enable swap is now fully idempotent too, so the reason
for the initial implementation is also solved.

Change-Id: I7be78780505f14fb1b581d22d4762a34cd2005d8

tests/roles/bootstrap-host/tasks/prepare_loopback_swap.yml

@@ -13,48 +13,56 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- block:
-    - name: Check if swap is already enabled
-      command: grep /openstack/swap.img /proc/swaps
+- name: Create swap file
+  command: "{{ swap_create_command }}"
+  args:
+    creates: /openstack/swap.img
+  register: swap_create
+  tags:
+    - swap-file-create
 
-  rescue:
-    - name: Create swap file
-      command: "{{ swap_create_command }}"
-      args:
-        creates: /openstack/swap.img
-      register: swap_create
-      tags:
-        - swap-file-create
+- name: Set swap file permissions to 0600
+  file:
+    path: /openstack/swap.img
+    mode: 0600
+  tags:
+    - swap-permissions
 
-    - name: Set swap file permissions to 0600
-      file:
-        path: /openstack/swap.img
-        mode: 0600
-      tags:
-        - swap-permissions
+- name: Format the swap file
+  command: mkswap /openstack/swap.img
+  when: swap_create | changed
+  tags:
+    - swap-format
 
-    - name: Format the swap file
-      command: mkswap /openstack/swap.img
-      when: swap_create | changed
-      tags:
-        - swap-format
+- name: Ensure that the swap file entry is in /etc/fstab
+  mount:
+    name: none
+    src: /openstack/swap.img
+    fstype: swap
+    opts: sw
+    passno: 0
+    dump: 0
+    state: present
+  tags:
+    - swap-fstab
 
-    - name: Ensure that the swap file entry is in /etc/fstab
-      mount:
-        name: none
-        src: /openstack/swap.img
-        fstype: swap
-        opts: sw
-        passno: 0
-        dump: 0
-        state: present
-      tags:
-        - swap-fstab
-
-    - name: Bring swap file online
-      command: swapon /openstack/swap.img
-      tags:
-        - swap-online
+- name: Bring swap file online
+  shell: |
+    return_code=0
+    if ! grep /openstack/swap.img /proc/swaps; then
+      swapon /openstack/swap.img
+      return_code=2
+    fi
+    exit ${return_code}
+  register: _set_swap_online
+  changed_when: _set_swap_online.rc == 2
+  failed_when: _set_swap_online.rc not in [0, 2]
+  # We skip ansible lint testing for this task as it fails with
+  # ANSIBLE0014 Environment variables don't work as part of command
+  # which is nonsense.
+  tags:
+    - skip_ansible_lint
+    - swap-online
 
 - name: Set system swappiness
   sysctl: