CBQE-948 Add phase timestamp info to event db in seriesly

The graphing script of cbmonitor will connect to event db to
get the phase timestamp, then it is able to graph phase by phase
by limiting the time range in seriesly database

Change-Id: I295e361a84ae2ec8a9c54080dc857505e7d97233
Reviewed-on: http://review.couchbase.org/23793
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chisheng Hong <chisheng@couchbase.com>
Tested-by: Chisheng Hong <chisheng@couchbase.com>