SOLR-5608: Harden test.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1559600 13f79535-47bb-0310-9956-ffa450edef68
SOLR-5608: Raise wait for leader timeout from 1000 to 15000

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1559609 13f79535-47bb-0310-9956-ffa450edef68