Fix python prereq install task

It's not possible to check ansible_pkg_mgr yet because we haven't
gathered facts. This patch adjusts the task to run on all distros
but it only has an effect on Ubuntu systems without python installed.

Change-Id: I8859b740a4d190fb1548af7ed7df92c248e2c5a3

playbooks/openstack-hosts-setup.yml

@@ -13,6 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+# NOTE(mhayden): CentOS always has python (because of yum), but it's possible
+# that Ubuntu nodes may not have python by default. Ansible doesn't work very
+# well if Python isn't installed.
+#
+# Also, we can't use a 'when' to check for the ansible_pkg_mgr here because
+# we haven't gathered facts yet.
 - name: Install Ansible prerequisites
   hosts: "{{ openstack_host_group|default('hosts') }}"
   gather_facts: false
@@ -20,9 +26,13 @@
   pre_tasks:
     - name: Ensure python is installed
       register: result
-      raw: apt-get -y install python
-      when:
-        - ansible_pkg_mgr == 'apt'
+      raw: |
+        if which apt-get >/dev/null && ! which python >/dev/null ; then
+          apt-get -y install python
+          exit 2
+        else
+          exit 0
+        fi
       changed_when: "result.rc == 2"
       failed_when: "{{ result.rc not in [0, 2] }}"