Test that we always cache index and bloom blocks

This is a unit test that should have been part of HBASE-4683 but was not committed. The original test was reviewed as part of https://reviews.facebook.net/D807. Submitting unit test as a separate JIRA and patch, and extending the scope of the test to also handle the case when block cache is enabled for the column family. The new review is at https://reviews.facebook.net/D1695.