LUCENE-5761: upgrade note for solr (merge r1603227)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1603228 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6175: Fix failing test by removing assert that matches exception message. They might be different between platforms.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1603234 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6175: Assert that exception message is not null

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1603237 13f79535-47bb-0310-9956-ffa450edef68