SOLR-6402: Only exit the thread loop on a KeeperException if it's expiration.

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1619792 13f79535-47bb-0310-9956-ffa450edef68

solr/core/src/java/org/apache/solr/cloud/OverseerCollectionProcessor.java

@@ -346,8 +346,6 @@ public class OverseerCollectionProcessor implements Runnable, Closeable {
             return;
           }
           SolrException.log(log, "", e);
-          throw new ZooKeeperException(
-              SolrException.ErrorCode.SERVER_ERROR, "", e);
         } catch (InterruptedException e) {
           Thread.currentThread().interrupt();
           return;