Correct muranoclient service_get function

{env_id}/services/{service_id} was using Manager._list instead of
Manager._get, resulting in an error processing the return value
(a dictionary). Patch changes it to use _get and adds a shell function
to test it.

Further work should be done on the services API since it's not terribly
useful without massaging the response data.

Change-Id: Icd0c1b92aac7185d099e050b5cd42ad23317afb2
Closes-Bug: #1326382
Merge "Correct muranoclient service_get function"