Add the ability to check the IAM policy linked to a spanner instance

[lhasadreams]

Detailed Description

Provide a new Resource that allows InSpec to test the data returned from:
gcloud spanner instances get-iam-policy --format json

Context

To test the IAM policy on a spanner instance

I consulted with @skpaterson on this.

[lhasadreams]

@slevenick @skpaterson Please can I get you view on this.
Cheers
Adrian

[sukchomb-zz]

Hi,

Would appreciate if this could be done at the earliest as our project has aggressive timelines to meet before X-mas.

Cheers,

Sukhjit

[slevenick]

This is available in 0.23.1

See: https://github.com/inspec/inspec-gcp/blob/master/docs/resources/google_spanner_instance_iam_policy.md