Currently it isn't possible to set extra labels on pods that use
the labels snippet. This means users are required to fork the helm
repository for OpenStack services to add custom labels. Use cases
for this are for example injecting Istio sidecars.
This change introduces the ability to set one set of labels on all
resources that use the labels snippet.
Change-Id: Iefc8465300f434b89c07b18ba75260fee0a05ef5
4340e272d7