'Creates a test directory and places OLI config there
Note that this is a class method. There can only be one test
directory at a time. OLITestLib is not suited for running
several tests in parallel.  The user is responsible for
cleaning that up herself.'

@classmethod
def create_test_dir(cls, suffix=''):

    assert (cls.cred_file != None)
    cls.testdir = os.path.abspath(tempfile.mkdtemp(prefix=('tmp_%s_' % suffix), dir=os.path.dirname(cls.cred_file)))
    cls.write_config_file()
    return cls.testdir
