provider/ec2: add unit and feature tests for provisioning instances with spaces in constraints

[Dimiter Naydenov]

With this PR: https://github.com/juju/juju/pull/3319, the EC2 provider respects the SubnetsToZones StartInstanceParams field (populated by the provisioner worker when spaces constraints are specified) and provisions instances in the given space's subnets, rather than all available zones (or a subset thereof - depending on the machine distribution group). This behavior is currently only manually live-tested - it needs better unit and feature tests.

[Dimiter Naydenov (dimitern)]

This bug report also assumes the suggestions from this RB review are also implemented: http://reviews.vapour.ws/r/2700/

[Anastasia (anastasia-macmood)]

As this is a tech-debt item, I am lowering its priority and removing it from a milestone.

[Canonical Juju QA Bot (juju-qa-bot)]

This bug has not been updated in 5 years, so we're marking it Expired. If you believe this is incorrect, please update the status.