dlm: print log message when cluster name is not set

Print a message when a cluster name is not specified by
the caller.  In this case the cluster name configured
for the dlm is used without any validation that it is
the cluster expected by the application.

Signed-off-by: Zhu Lingshan <lszhu@suse.com>
Signed-off-by: David Teigland <teigland@redhat.com>