SquidUpdate debug message are now in 'squid' group

To debug purging issues in beta, it would be useful to have all squid
related messages grouped at the same place.  wfDebug() is logged on beta
but it has a good amount of spam which is not that useful.  Regrouping
all squid operations under the debug log group 'squid' will make it
easier to investigate.

Change-Id: I11112585f38307ae56ec3e05e7a8d6d9dab31bfa
Merge "SquidUpdate debug message are now in 'squid' group"