getLogger()->log format string errors

This issue was reported from Aliaksey:

Hi,

Today I came across a place in ep-engine where wrong number of
parameters was passed to getLogger()->log() call. Thus I decided to
enable gcc format string checks (patch is on gerrit:
http://review.couchbase.org/14901). I had to fix few errors in
memcached. But there's a whole bunch of such errors in ep-engine.
Including pretty harmful like passing more arguments or less arguments
than it's required by a format string. Could you please fix this when
you have some free time?

Thanks,
Aliaksey.