A little clean up for initial agent logging.

A little clean up for initial agent logging.

Now that we have a logging worker that will set the log
levels to the system wide setting when it starts, we can
start all new agents with debug, and then as soon as the
agent starts, it will change it.

A drive by fix here to have the machine agent explicitly
remove the logfile writer from loggo if one has been set.
Machine agent upstart jobs that are around from before 1.16
will otherwise cause duplicate lines.

https://code.launchpad.net/~thumper/juju-core/logger-initial-state/+merge/185962

(do not edit description out of merge proposal)

[thumper, 2013-09-17 02:03:35]

Please take a look.

[wallyworld, 2013-09-17 02:15:53]

LGTM, although I'd prefer to see an integration style test that confirms that
debug is used and then turned off as expected. We do this sort of thing
elsewhere for other similar "live" sets of tests.