Fix race condition in test 06-main-compaction.t

Ensure that automatic cleanup is disabled before adding
partition for cleanup and verifying the index state was
updated to reflect that state transition.

Change-Id: I1334f4ac0e851fa754ec0d28468ea3134d5150fa
Reviewed-on: http://review.couchbase.org/24012
Tested-by: Filipe David Borba Manana <fdmanana@gmail.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Reviewed-by: Filipe David Borba Manana <fdmanana@gmail.com>