Add keystone code to capture and ignore warning

When upgrading to grizzly, I found many errors
in the keystone command line output.The provider
was unfortunately not robust enough to still
parse STDOUT when these error appeared.

This commit wraps all keystone CLI invocations
in something that filters out warnings.
explicitly set token_format

the default setting for token_format in grizzly
changes from UUID to PKI.

This adds explicit configuration to ensure that
it is set as UUID to ease the process of upgrades
and allow the same puppet code to work with both
versions.