use collection and environment variables as fallbacks for common auth vars across all roles

[mikemorency]

This is feedback from the testathon.

Each role uses a similar set of authentication variables for things like vcenter hostname, username etc. Instead of requiring users to set these variables for all roles individually, it was recommended we have a centralized option.

This change allows people to set a collection level variable or an environment variable to set authentication options for everything. If the user needs to set a value for a specific role, they can still do that. The role variables take the highest priority

[bardielle]

Please change the integration tests to use the new env vars