locktest: consolidate do_lock and do_unlock, and add ability to F_GETLK

locktest: consolidate do_lock and do_unlock, and add ability to F_GETLK

Eliminate do_unlock as it's just cut-and-paste of do_lock (down to the
bad stderr fprintf). Fix the debug messages to print the cmd and type,
and add the ability to do a WRTEST and RDTEST.

Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>