MB-5264: using persisted Checkpoint ID to ensure full commit
MB-5264: using persisted Checkpoint ID to ensure full commit

In this change-set, to ensure full commit, XDCR will create a new
checkpoint in ep engine and wait till the persisted checkpoint ID
catch up with the new checkpoint ID. Command CMD_CREATE_CHECKPOINT
is introduced in ns_server to send command to ep engine to create
the new checkpoint and get its ID.

Change-Id: I1d1755cfc8ef578299815ff213d5ecbfa2d187d0
Reviewed-on: http://review.couchbase.org/17100
Tested-by: Junyi Xie <cec9b1c9f34a8d92cba938f3f3364d5120580782@gmail.com>
Reviewed-by: Damien Katz <99e6b749acbfbe2a596df99e91d24d6e1fdbee00@couchbase.com>

daverigby/ns_server,ceejatec/ns_server,t3rm1n4l/ns_server,daverigby/ns_server,membase/ns_server,ceejatec/ns_server,ceejatec/ns_server,pavel-blagodov/ns_server,membase/ns_server,pavel-blagodov/ns_server,pavel-blagodov/ns_server,mschoch/ns_server,mschoch/ns_server,t3rm1n4l/ns_server,mschoch/ns_server,membase/ns_server,mschoch/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,pavel-blagodov/ns_server,daverigby/ns_server,ceejatec/ns_server,vzasade/ns_server,mschoch/ns_server,nimishzynga/ns_server,t3rm1n4l/ns_server,vzasade/ns_server,ceejatec/ns_server,daverigby/ns_server,mschoch/ns_server,membase/ns_server,membase/ns_server,ceejatec/ns_server,vzasade/ns_server,vzasade/ns_server,nimishzynga/ns_server,membase/ns_server,nimishzynga/ns_server,daverigby/ns_server,t3rm1n4l/ns_server