features/changelog : Improvement in changelog "encoding-change".

change in encoding method of changelog was critical section for
"fop dispatch thread", "roll-over thread" and "reconfigure dispatch thread".

In this patch the "encoding-method" is changed by the reconfigure dispatch thread
lazily during handle_change, which solves the concurrency among the racing
threads.

BUG: 1002940
Change-Id: I78c3e8887efa46d0fcc60755cdf4243031cfa3eb
Signed-off-by: Ajeet Jha <ajha@redhat.com>
Reviewed-on: http://review.gluster.org/5844
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>