geo-rep: Consume Changelog History API

Every time when geo-rep restarts it first does FS crawl using
XCrawl and then switches to Changelog Mode. This is because changelog
only had live API, that is we can get changes only after registering.

Now this(http://review.gluster.org/#/c/6930/) patch introduces History
API for changelogs. If history is available then geo-rep will use it
instead of FS Crawl.

History API returns TS till what time history is available for
given start and end time. If TS < endtime then switch to FS Crawl.
(History => FS Crawl => Live Changelog)

If TS >= endtime, then switch directly to Changelog mode
(History => Live Changelog)

Change-Id: I4922f62b9f899c40643bd35720e0c81c36b2f255
Signed-off-by: Aravinda VK <avishwan@redhat.com>
Reviewed-on: http://review.gluster.org/6938
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Humble Devassy Chirammal <humble.devassy@gmail.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
[glusterd/snapshot] Glusterd crashes when a same command
eg snapshot create is fired simultaneously on a node

Cause: In glusterd_mgmt_v3_initiate_snap_phases() , the function
glusterd_mgmt_v3_post_validate() asserts on the NULL value of
req_dic. req_dic is not initialized as
glusterd_mgmt_v3_initiate_lockdown() is not able to acquire the lock
and comes to the "out" section, before initializing req_dic
(via glusterd_mgmt_v3_build_payload)

Fix: Call glusterd_mgmt_v3_post_validate() only if the lock is
acquired.

Change-Id: I7cb55b6c0013ad1c8bbb922a62c34aab097bafe9
BUG: 1090047
Signed-off-by: Joseph Fernandes <josferna@redhat.com>
Reviewed-on: http://review.gluster.org/7500
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>