register_all_nodes() now accepts keystoneclient

os_cloud_config.nodes.register_all_nodes() was a little bad in the
fact that it would warn that it was creating a Keystone client, but
you couldn't pass one in to silence the warning. Since this warns
everytime register-nodes is run, silence it.

Change-Id: I5e70df9a91f53f706e414ed041270f2c620977d2
Merge "register_all_nodes() now accepts keystoneclient"