Correcting error in NeutronClientRemoteWrapper._get_adapters

changes
* fixing the list comprehension in _get_adapters when aggregating all hosts
* adding tests for _get_adapters to test initial add of adapter and
  returning all adapters

Change-Id: I13c8b5a85c312a39a6b5d567390782cecef1ce9c
Closes-Bug: #1383904
Merge "Correcting error in NeutronClientRemoteWrapper._get_adapters"