Improved juju get help
Merge pull request #1166 from dimitern/lp-1392544-better-docs-for-juju-get

Improved juju get help

According to this bug http://pad.lv/1392544 the output
of "juju get" was somewhat confusing because the "default"
field in the output looks the same as "default" field in
the charm config definition, but they mean different things.

(Review request: https://reviews.vapour.ws/r/477/)