Adds KMIPSecretStore and unit tests

This adds a KMIP implementation of SecretStore. This implementation will use
a KMIP server backend to store secrets. Additionally, this patch adds unit
tests that are in a format similar to the rest of the OpenStack projects.

Implements the SecretStore abstraction from:
    https://review.openstack.org/#/c/94710/

Change-Id: Id39b6c84d0990369e2f535f22826cd41708a2f63
Implements blueprint kmip-secret-store
Merge "Adds KMIPSecretStore and unit tests"