Clean up: add the traditional pre-processor safety check in headers under

Clean up: add the traditional pre-processor safety check in headers under
utils/mount to prevent them from being included multiple times.

For headers that already have this, use a more unique macro name to reduce the
probability that some other header may use the same macro.

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