SOLR-6633 field name changed from _src to _src_ by populafr demand

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1644103 13f79535-47bb-0310-9956-ffa450edef68
fix test bug

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1644124 13f79535-47bb-0310-9956-ffa450edef68
SOLR-6633 changing the field name from \_src to \_src\_

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_5x@1644136 13f79535-47bb-0310-9956-ffa450edef68