daemon logging: unifying output and timestamps

A little refactor of the ./pkg/log so engine can have a logger instance

Signed-off-by: Vincent Batts <vbatts@redhat.com>


ping @shykes @vieux @crosbymichael  for the ./docker and ./pkg/log changes
ping @crosbymichael for the ./pkg/iptables changes
ping @shykes for the ./engine changes

ping @tiborvass since he and i conspired ... :tongue: 
I guess it's easier for scripting: merging logs and then sorting them would be possible if the first thing is the timestamp