Fix connection management for noTimeoutClient

1. Don't share a connection pool between `DefaultDockerClient.client` and
   `noTimeoutClient`. Each Jersey client should have its own connection pool.

2. Shut down `noTimeoutClient` as part of `DefaultDockerClient.close`, just
   like we do for the default client.

3. Get rid of an `ExecutorService` that is no longer being used.
If this throws an exception, I think we'll leak the 2 connection managers and other client because my guess is no one will call close. We should probably wrap all 4 objects in a try/catch so we can call close on them if an exception is thrown.