Incorrect credentials use for healthcheck when multiple saved credentials exist for the same cloud

[nuwang]

Steps to recreate:

1. Save two sets of credentials for an OpenStack cloud, each in a different project (say projectA, and projectB).
2. Set credentials for projectA as default
3. Launch an instance using projectB credentials.

Expected:
The health check will use the non-default projectB credentials and healthcheck should succeed.

Actual:
The health check uses the default projectA credentials, and the healthcheck status says unknown. Should it say deleted instead?

Possible solutions:
We don't have an association between a deployment and a set of credentials. We could add an optional relationship to credentials.