Official OpenStack clients commonly support specifing a client
certificate/key to enable SSL client authentication when communicating
with OpenStack services. This patch enables such feature in Terraform
with new parameters and environment variables:
* 'cert' provider parameter or OS_CERT env variable to specify client
certificate file,
* 'key' provider parameter or OS_KEY env variable to specify client
certificate private key file.
This commit enables the ability to authenticate to OpenStack by way
of a Keystone Token. Tokens can provide a way to use Terraform and
OpenStack with an expiring, temporary credential. The token will need
to be generated out of band from Terraform.
Joe Topjian