Fix Timekeeper Bookkeeping While Merging Streams

Initial stream gets merged to Maint Stream after initial build
is done. Timekeeper bookkeeping needs to handle that.

Change-Id: I30ad6d8dcd0cdbb103000064c9c8ec6d21988e08
Reviewed-on: http://review.couchbase.org/43614
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>