hypervisor: use stdlib for cinder ceph key

To avoid resource dupplication errors in Puppet, we use here stdlib and
ensure_resource, to allow us to declare on the same node a Cinder volume
server with RBD driver and a compute using Ceph also.

Bug #402
cinder keyring: align cinder & nova permissions

Set same permissions on the same resource to avoid conflicts when puppet
compiles the catalog.

Bug #402
keyring: use a specific group for permissions

- create a group 'cephkeyring'
- ensure nova and cinder are part of this group.

Note: I don't use Puppet to manage the users, since it's already managed
by puppet-cinder and puppet-nova.

Bug #402
keyring: clean method to add a group

Add 'nova' and 'cinder' users to 'cephkeyring' group using a better way,
more "Puppetist"

Bug #402
cephkeyring POSIX group: use usermod

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
ceph keyring: manage group via virtual resource

Manage the group membership with a Puppet Virtual Resource.

Bug #402
keyring: fix typos

Bug #402
keyring: use 0440 for permissions

Bug #402
Merge pull request #403 from enovance/bug/402/emilien

Improve Ceph Keyring files management