Support multiple outputs based on platform/test suite variables (issue 121)

[jcastillocano]

Hi,

in order to workaround issue #121 we came up with this implementation: support template format for verifier.output parameter. Right now only platform and suite are supported, but it easy to add more parameters if they are needed.

Default output is not modified, as well as custom path option. The only behavior updated here is when you define the output as format string (%{}), so given platform or suite flags they will be replace (in that way, you can specify an output value in the general verifier section, but multiple inspec files will be created based on the flags.

Added unit test and README block explaining this feature.

Thanks @AgarFu for your help!

[AgarFu]

👍

[chris-rock]

@jcastillocano Great work. This PR implicitly manifest the decision that we are using the sprintf method of Ruby https://ruby-doc.org/core-2.2.0/String.html#method-i-25 instead of any ERB templates. I think that is working well, since yml have key-value pairs only.

Could you do me one favor and squash the commits?

[jcastillocano]

Thanks @chris-rock!

[florian-asche]

Would be cool to have "instance" also as possible parameter. If you use kitchen-list and create a loop for that data in jenkinsfile you cannot use suite/platform because of different names. Dots will be removed and - to _. Instance should be correct.