Fix fallback name for ocf_attribute_target

For bundles, various resource agents now use ocf_attribute_target to
get the name of the pacemaker node to store attributes on.

If a recent version of the resource agent is being run on a pacemaker
version which does not support bundles, ocf_attribute_target will
return an empty string as hostname.

Provide a fallback path so the resource agent gets a valid name when
the resource is not containerized.