fix c_str error when connecting to MySQL

Former-commit-id: 6c3fe3ff323cd8baa045d00f343bd48de312aa41

cpp/CHANGELOG.md

@@ -37,6 +37,7 @@ Please mark all change in change log and use the ticket from JIRA.
 - MS-110 - Avoid huge file size
 - MS-148 - Disable cleanup if mode is read only
 - MS-149 - Fixed searching only one index file issue in distributed mode
+- MS-153 - fix c_str error when connecting to MySQL
 
 ## Improvement
 - MS-82 - Update server startup welcome message