tryBuildIndex() can submit all pending index builds at once due to negative quota

There are several problems in lifecycle.go's tryBuildIndex() function:

1. A partitioned index can cause newQuota to go negative, because every partition in INDEX_STATE_READY decrements this, whereas it should only be decremented once for the entire index. The negative quota will then trigger submission of all pending index builds at once.
2. If the batchSize config parameter is reduced, this can also cause a negative newQuota value to occur with same side effect.
3. If background build is disabled, a partitioned index will append defnId back onto pendingList N times instead of just once, where N is the number of partitions.