glusterd: sanitize gsyncd config option validation
glusterd: sanitize gsyncd config option validation

- rely on --config-check functionality of gsyncd to find out if option exists
- maintain a list of those options with which we don't want the user to fiddle with
  (glusterd internals imply these so it' just the proper component for it)
- fail if user does a set/del on these

Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Anand Avati <avati@gluster.com>

BUG: 2659 (gsync config-del option is not working properly)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=2659

Kaushikbv/Gluster,Kaushikbv/Gluster,Kaushikbv/Gluster