Fix ClassCastException and AIOOBE in TestSolrConfigHandlerConcurrent

Noticed some weird errors in the logs for TestSolrConfigHandlerConcurrent:

1. Test starts a thread to change each cache listed in the query section of the config but 4 of the keys inside the query section do not contain a cache definition at all. The thread would start and immediately exit when trying to cast the long value to a Map.
2. The second half of the invokeBulkCall method is never executed because it tried to do {{ String url = urls.get(urls.size());}} which will always result in an AIOOBE and the thread would (silently exit)
3. The second half also contained a bug where a string was being asserted to be equal to a long object so after fixing #2 above, the test always failed.