MB-11490 Close open tmpfile fds before starting native view updater

All open sort tmpfile fds should be closed before starting the native
view updater. Observed few failures recently with error codes such as
COUCHSTORE_ERROR_OPEN_FILE, COUCHSTORE_ERROR_NO_SUCH_FILE and
COUCHSTORE_ERROR_READ while updater operating on sort tmpfiles.

Change-Id: Ia3140131b2968ab78971e3e7d4aaf899dfc40e97
Reviewed-on: http://review.couchbase.org/38630
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>