MB-12572 Sync the view group after upgrade

During offline upgrade of couchbase, if seqs are empty([]) in the
group, initial build will happen after upgrade and that will set
partition version list to nil.We should sync the group after upgrading
the header, so that partition version list will not be nil after
initial build.

Change-Id: I3eb5114d69dc2c8087310b59d28ff3e01e6ef5e2
Reviewed-on: http://review.couchbase.org/43048
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: buildbot <build@couchbase.com>