'List all credentials for a user.
:param user_id: id of user
:returns: credentials: list of ec2 credential dicts'

def get_credentials(self, user_id):

    self.identity_api.get_user(user_id)
    credential_refs = self.credential_api.list_credentials_for_user(user_id, type=CRED_TYPE_EC2)
    return {'credentials': [self._convert_v3_to_ec2_credential(credential) for credential in credential_refs]}
