MB-10259: Increase max number of threads AtomicQueue supports.

Increase the limit from 100 to 500 to handle large number of CPU
cores. Also added an assert if this limit is exceeded.

Change-Id: If9445a8c91c0daf9475a711145cccc7de8986e53
Reviewed-on: http://review.couchbase.org/34699
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>