Add ignore_errors to fix minor bug with fallback source for apt-key.
Add ignore_errors to fix minor bug with fallback source for apt-key.

Add ignore_errors to execute 'add galera apt-keys using fallback source'.
Bug was found and described by David Wilde.

Change-Id: I22f68fd78161498d636972f3181031da093daf7d
Closes-Bug: 1594467
Co-Authored-By: David Wilde <5a42981a85400abd2a7c4a3918a9ab2eb8df2a5c@rackspace.com>

openstack/openstack-ansible-galera_client,openstack/openstack-ansible-galera_client