glusterd: Don't persist enable-pump in volinfo->dict

- enable-pump option in the pump xlator is set during a replace-brick
  session. This was persisted in the volinfo->dict for volume file
  generation.
  It has two 'harmful' side-effects,
  a) It would lead to volinfo cksum divergence among peers in
     cluster (for the same version no.) during a replace-brick session.

  b) "enable-pump" key would appear in "gluster volume info VOLNAME".
     This key is used internally in volume file generation code to
     optionally load the pump xlator in the source brick. It is _not_
     an volume option.

Change-Id: I37a8e7186e2985d187e4a166a599cf69145a90f9
BUG: 886000
Signed-off-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-on: http://review.gluster.org/4367
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>