Indicate whether service is down for mc driver

memcache driver for service didn't log any clue
whether the service is down or not. This patch add a
log to indicate it at DEBUG level.

Closes-Bug: #1382564

Change-Id: I05e12b56411f4475d1ef50e90e09abf75d7355b0
Merge "Indicate whether service is down for mc driver"