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

Currently, a timeout for MySQL client is hard coded(10 seconds) and operation error is occured when MySQL server does not respond to MySQL client in 10 seconds whatever user set a long timeout for operation.

This patch disable a timeout for MySQL client to resolve above problem.
Merge pull request #495 from knakahira/fix-mysql-client-timeout

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