Unit test refactoring/MOBSDK-582

As explained in my mail:
- all run<xxxx>test methods were removed and replaced with setUp/tearDown.
- for tests being run in XCode, go to 'Edit Scheme->Run' and select arguments. In the environment variables section add TEST_SERVER_PLIST with JUST the name e.g. test-server_version3.plist (including $HOME didn't seem to work).
- run_test<xxx>.sh scripts have been included that can be used from command line and/or Bamboo
- MOBSDK-582: the error description is being filled with the error code response. For that purpose 2 additional error codes have been defined (also in the spec).