MB-9307: Add indexer rollback

Add the functionality to rollback to a certain sequence
number of a certain partition. It rolls back to a previous
header, which means that other partitions might also be
rolled back.

"make check" is epected to fail and is fix with the next
commit.

Change-Id: I62cae905fd3e6e733310057e36a3f66c7200d315
Reviewed-on: http://review.couchbase.org/29732
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>
Tested-by: Volker Mische <volker.mische@gmail.com>