mountd: Fix up version and usage messages

Clean up: rpc.mountd is no longer known as kmountd.  Use the program's
basename rather than the full pathname for the usage message.  Display
a version message at start up similar to statd's.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>