Send unnecessary error message to /dev/null

deploy/common.sh

@@ -3,7 +3,8 @@
 cleanup(){
     name=$1
     set +e
-    docker rm -vf ${name}
+    echo clean up ${name} if exists
+    docker rm -vf ${name} > /dev/null 2>&1
     set -e
 }
 

deploy/longhorn-deploy-node.sh

@@ -49,7 +49,7 @@ if [ "$port" != "" ]; then
 fi
 
 set +e
-iscsiadm_check=`iscsiadm --version 2>&1`
+iscsiadm_check=`iscsiadm --version > /dev/null 2>&1`
 if [ $? -ne 0 ]; then
         echo Cannot find \`iscsiadm\` on the host, please install \`open-iscsi\` package
         exit 1