Add logging

[LCVcode]

Adding logging will be an important method for tracking jockey usage. We need to understand the frequency of usage as well as the kinds of commands that are run. We can probably put logs in /var/log/juju/jockey, or something like that.

Logging throughout would be nice, but logging on CLI calls is essential.

It would make sense to add logging levels as a CLI option, once we know logging works.

[johnlettman]

Unlinked #47 since it's only CLI logging.