Allow selection of target cloud using environment variables

[sudeephb]

If there are two or more clouds associated to a single controller, zaza chooses one of the clouds by itself to deploy the test models. It is possible to specify a particular cloud using the zaza config file. It would be convenient to be able to set an environment variable like ZAZA_CLOUD_NAME to specify the cloud where the models for testing will be deployed.

[ajkavanagh]

I think this opens up an interesting question of reviewing how zaza gets its configuration. It would probably be nice to be able to specify config via:

• command line arguments.]
• the zaza config file
• via environment variables prefixed with ZAZA_

If a common set of variable names existed across all three mechanisms, then it would become much easier to understand how to configure zaza before a test run.

Back to this request: yes, I see this as a useful addition, where the env variable would override the config file (if it existed).