added dry run support for upgrade-juju
simplified upgradejuju dry run test
changed upgrade-juju dry run option to --dry-run
added log to intruct the user how to run this command to update to a particular version
made output prettier based on fwereade's feedback
removed commented out line in upgradejuju_test
Merge pull request #64 from mattyw/upgrade-dry-run

added dry run support for upgrade-juju

Fix for https://bugs.launchpad.net/juju-core/+bug/1272544.

Added a --dry flag to the upgrade-juju command. When --dry is specified the action to be taken is output to Stderr. Added two tests to check that this information gets output and that the agent version's aren't changed after running the command with --dry