Use mysql command to detect the health of instance

1. Create running? method for WardenService
2. Bump mysql2 gem upto 0.3.11 so that Mysql2::Client
  won't blocks ruby process
3. Wrap Mysql2::Client.new into a Timeout. To make sure
  client connection won't takes too long.
4. Fix few warnings

Change-Id: I3d248a8e08259807dabe9fb2773bab95aa18962c
Merge "Use mysql command to detect the health of instance"