glusterd-volgen: Improve volume op-versions calculation

Volume op-versions calculations now take into account if an option,
 a. enables/disables an xlator, or
 b. is a boolean option.
This prevents op-versions from being updated when a feature is disabled.

Also, correctly close the dynamically loaded xlators in
xlator_volopt_dynload() and prevent leaks.

Change-Id: I895ddeeec6f6a33e509325f0ce6f01b7aad3cf5c
BUG: 954256
Signed-off-by: Kaushal M <kaushal@redhat.com>
Reviewed-on: http://review.gluster.org/4952
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>