Retry when connection to cinder is refused

Currently, cinder client does not retry when connections to cinder
service is refused. There are many legitimate scenarios under which
retry should be attempted:
1) cinder service being restarted;
2) cinder service is running on multiple API nodes behind a LB, which
might be temporarily overwhelmed or being maintained.

In any scenario, retry with a backoff timer does not seem to hurt.

Change-Id: I3c290c59fa67262c4a3473815b4380ee39e24332
Closes-Bug: 1347843
Merge "Retry when connection to cinder is refused"