This patch ensures that the authorized_keys ansible module, as well as
the built in "generate_ssh_keys" flag for user creation, so that we can
avoid using shell out commands.
Additionally, this moves the key synchronisation to use ansible
variables instead of the memcache server.
Change-Id: Icd97ebd44f6065fc60fdce1b61e9dc2daa45faa0
Closes-Bug: #1477512