MB-11563 Update partition versions during updater checkpointing

The updater performs batch writes. After each short disk batch writes,
it will synchronize new header information and partition sequence numbers
upto which it has processed for each partitions. The view_group receives
the new header, seqnos and update the group header. We updated partition
versions for each partitions only after the complete updater instance run.

When new passive partitions are added to the current index as part of partition
migration from another node to current node, we have an way to notify newly
added passive partiton list to the currently running updater. This ensures that
updater doesn't need to be killed and restarted again with newly added passive
partitions, thereby wasting useful indexing time. When the updater receives
the new passive partitions list, it will start streaming changes from those
partitions by the updater-loader. When the updater checkpoints after it
received a new passive partition, it will be still sending a old partition
version list as part of new header. The view_group's updater checkpoint processor
calculates the missing partitions by checking which are the partitions which
are not present in checkpointed group's vbucket seqnos list. Since the seqnos
list contains the newly added passive partition, we will not be doing any
addition of that partition's entry in the partitions versions list. So the
view group's partitions version list has those passive partitions missing now.

At this instance if a higher priority happens, the view group terminates the
current updater instance (Remember that the correct partitions versions list
is only updated after complete updater run.). Hence nobody is going to fix
the partitions versions list and it can have missing passive partitions.

Eg.
Updater has partition verion list: [{1, v1}, {2, v2}]
Added new passive partition 5 and updater processed it.
Updater checkpointed new group,
seqnos list: [{1, 23}, {2, 23}, {5, 10}]
part versions list: [{1, v1}, {2, v2}]
View group kills updater due to higher priority task and now partition versions
list has missing entries.

Fixed updater to store partition versions for newly added partitons and send
upto date partitions versions list during checkpointing.

Change-Id: Ia47417e0d37429cc22dc41d826532b71ca116471
Reviewed-on: http://review.couchbase.org/38931
Reviewed-by: Sarath Lakshman <sarath@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Nimish Gupta <nimish@couchbase.com>
Tested-by: buildbot <build@couchbase.com>