SOLR-10471: update default zk session timeout in bin/solr* scripts

* zkClientTimeout value is already set to 30s in solr.xml but
  same update was missing from bin/solr* script

solr/CHANGES.txt

@@ -249,6 +249,9 @@ Other Changes
 * SOLR-14579: Comment SolrJ 'Utils' generic map functions 
   (Megan Carey and a lot of education from Uwe Schindler via Erick Erickson)
 
+* SOLR-10471: Update default Zookeeper session timeout to 30s in bin/solr and bin/solr.cmd
+  (Michael Braun, Markus Jelsma via Munendra S N)
+
 ==================  8.6.2 ==================
 
 Consult the LUCENE_CHANGES.txt file for additional, low level, changes in this release.

solr/bin/solr

@@ -2037,7 +2037,7 @@ fi
 
 if [ "$SOLR_MODE" == 'solrcloud' ]; then
   if [ -z "$ZK_CLIENT_TIMEOUT" ]; then
-    ZK_CLIENT_TIMEOUT="15000"
+    ZK_CLIENT_TIMEOUT="30000"
   fi
 
   CLOUD_MODE_OPTS=("-DzkClientTimeout=$ZK_CLIENT_TIMEOUT")

solr/bin/solr.cmd

@@ -1143,7 +1143,7 @@ IF [%SOLR_LOG_PRESTART_ROTATION%] == [true] (
 IF NOT "%ZK_HOST%"=="" set SOLR_MODE=solrcloud
 
 IF "%SOLR_MODE%"=="solrcloud" (
-  IF "%ZK_CLIENT_TIMEOUT%"=="" set "ZK_CLIENT_TIMEOUT=15000"
+  IF "%ZK_CLIENT_TIMEOUT%"=="" set "ZK_CLIENT_TIMEOUT=30000"
 
   set "CLOUD_MODE_OPTS=-DzkClientTimeout=!ZK_CLIENT_TIMEOUT!"
 

solr/bin/solr.in.cmd

@@ -56,7 +56,7 @@ REM Leave empty if not using SolrCloud
 REM set ZK_HOST=
 
 REM Set the ZooKeeper client timeout (for SolrCloud mode)
-REM set ZK_CLIENT_TIMEOUT=15000
+REM set ZK_CLIENT_TIMEOUT=30000
 
 REM By default the start script uses "localhost"; override the hostname here
 REM for production SolrCloud environments to control the hostname exposed to cluster state

solr/bin/solr.in.sh

@@ -67,7 +67,7 @@
 #ZK_HOST=""
 
 # Set the ZooKeeper client timeout (for SolrCloud mode)
-#ZK_CLIENT_TIMEOUT="15000"
+#ZK_CLIENT_TIMEOUT="30000"
 
 # By default the start script uses "localhost"; override the hostname here
 # for production SolrCloud environments to control the hostname exposed to cluster state