Add --log-level support - Issue #5198

I noticed that even if I set the log level to 'fatal' there are still quite a few things printed to stdout/err.
In my quick scan its because not everything is using the default logger.  For example, I noticed that
job.go has its own.  I think that should be removed and everyone should use the same logger.
I could move that change into this PR if people want, but I'd prefer to split it out into a new one so that
this one is just focused on adding the --log-level flag.

Closes #5198

Signed-off-by: Doug Davis <dug@us.ibm.com>
Not necessarily.  Rather, what I'm trying to do is use constants the way they're supposed to be used - meaning, not assume I know what their value is and simply use the names instead.  So, yes as I mentioned in my other message, right now this seems odd to compare DebugLevel with InfoLevel because we know the answer, BUT if tomorrow if someone decides that Docker's default log level should be "fatal" or "some new level that's more verbose than debug - like debug++" then I don't want to require that person to have to remember to go looking for all of the places where we assumed the default value for dockers log-level was 'info' - which is what we'd be doing if I removed the if-stmt. As I said, this if making the code safer and not in some abstract way, this is using constants properly by not assuming I know their underlying values.