Packer debug

[pix]

The first patch adds a debug switch to allow viewing the packer template.
The second one, adds a --profile option (since prepare_config is now aware of args) to override the selected profile in config.js

[obilodeau]

--show-packer-template: I'm not fond of exposing a deep debugging option like that to the command-line.

In debug mode, malboxes will leave generated configuration files in the cache folder. That's how I check for issues. Maybe we can modify that behavior so that the generated packer.json will be shown on the command-line in debug mode instead?

--profile: I'm interested but let's see how the discussion in #77 evolves first.

[pix]

To be honest I submitted this pull request because I spent quite some time doing tests and having a fast way to show what would the packer config looked like was useful (hence the formating using json.loads/json.dumps)

Also when a build failed, a quick --show-packer-template (since the original was deleted) was kind of useful.

Maybe this should be a hidden switch ?

As for the profile I answered in #77

[obilodeau]

I'm willing to see the dump of the full json beautified config when in --debug mode but otherwise, I think either running tests or looking at cache folders should suffice. Thoughts?