Update LuceneSearchRequest maxqueue to 600

Been seeing some sporadic requests in the past month about the
queue being full. Bumping to 600 should give us some more headroom
without overloading things. It's still less than 800, which is the
point where we'd start to cause problems.

Change-Id: I80ddb3756899bdf74e077b566256230b28742943
Merge "Update LuceneSearchRequest maxqueue to 600"