logging format improvements

[Ian Booth]

juju log messages use a format like so:

<datetime> <severity> JUJU:<cmd> <msg text>

where, if command is a subcommand, it prints as <super cmd>:<cmd>

However, super command is always "juju" so that results in too much juju in the message.

<msg> often also contains text like "cmd/juju: blah blah", since it was logged like so:

log.Infof("cmd/juju: looking blah blah...")

Also, for the following situation:

2013/03/28 18:42:10 INFO JUJU:juju:publish charm sent; waiting for it to be published...

"publish" is the command name.. it's not the "publish charm".

We need to:

1. drop from the command name rendering the super command name

2. drop the ad hoc "cmd/juju" type text from log messages since the standard format now contains that information

3. add a separator between <cmd> and <msg> so that the command name and message are not confused.
.

[Dimiter Naydenov (dimitern)]

This was fixed in CL: https://codereview.appspot.com/8674043/