PSQLADM-511: proxysql-admin syncusers hangs at 1000 DB user or above

https://perconadev.atlassian.net/browse/PSQLADM-511

Follow-up fix:
Passwords having single quote (') characters were not processed
properly due to the missing of escaping.

proxysql-admin-common

@@ -663,6 +663,11 @@ function syncusers() {
 
     username=${user}
     password="${mysql_users_full_hash[${username}]}"
+
+    # Since we're using single quotes within the SQL statement, only need
+    # to escape the single quotes for SQL
+    password=${password//\'/\'\'}
+
     debug "$LINENO" "Processing MySQL user: '${username}'"
 
     # Check if the user exists in ProxySQL