Detect query timeouts and throw a specific exception

Detect query timeouts and throw a specific exception

Throw DBQueryTimeoutError if a database query error is detected
to be a timeout.

Only DatabaseMysqlBase has been updated here.

This is a subclass of DBQueryError, so existing catch'es will work.

Bug: T175775
Change-Id: I4749dc33ad530d9b22504f02106b1ca49e8eb167