Exact domain matching for organization data source

[c2thorn]

Fixes hashicorp/terraform-provider-google#6366

Release Note Template for Downstream PRs (will be copied)

Fixed an issue where data source `google_organization` would ignore exact domain matches if multiple domains were found

[modular-magician]

Hi! I'm the modular magician. Your PR generated some diffs in downstreams - here they are.

Diff report:

Terraform GA: Diff ( 1 file changed, 12 insertions(+), 2 deletions(-))
Terraform Beta: Diff ( 1 file changed, 12 insertions(+), 2 deletions(-))

[slevenick]

Confusing that display name is actually the domain name of the org...