Use WMCore's REST API

The old RESTInteractions, while nice, missed some pretty major
functionality, the least of which is the ability to cache requests.
Because of the number of round-trips to cmsweb (times transcontinental
latency), each CRABClient command takes much longer than it needs to
because it doesn't cache even simple requests like:

{'result': [{'services': ['/DC=ch/DC=cern/OU=computers/CN=vocms(24[345]|3[136]|21).cern.ch']}]} 200 OK False
{'result': [['3.3.7', '3.3.7.patch1', '3.3.7.patch2', '3.3.8', '3.3.8.rc10']]} 200 OK False

This wraps the WMCore api with a simple bit of argument-smashing to get
it to look like what the old API looked like and enables caching.