Medium: mysql: fix unexpected operation error that caused by MySQL client timeout.

Currently, a timeout for the MySQL client is hard coded(10 seconds) and operation error is occured when the MySQL server does not respond to the MySQL client in 10 seconds whatever user set a long timeout for operation.

To resolve this problem, I add a new parameter "client_timeout" and the default value is 0(timeout is disabled, the MySQL client waits for response from the MySQL server until the operation timeout is occurred).

If you have a explicit timeout requirement to understand the MySQL server as a failure, then set your timeout value to "client_timeout" parameter.