'Call ``POST /credentials`` for creating ec2 credential.'

def test_create_ec2_credential(self):

    (blob, ref) = unit.new_ec2_credential(user_id=self.user['id'], project_id=self.project_id)
    r = self.post('/credentials', body={'credential': ref})
    self.assertValidCredentialResponse(r, ref)
    access = blob['access'].encode('utf-8')
    self.assertEqual(hashlib.sha256(access).hexdigest(), r.result['credential']['id'])
    self.post('/credentials', body={'credential': ref}, expected_status=http_client.CONFLICT)
