bugfix: access results failed of Test API

bugfix: access results failed of Test API

File "/Users/fengxiaowei/opnfv/releng/utils/test/testapi/venv/lib/python2.7/site-packages/opnfv_testapi/resources/models.py", line 47, in format_http
return self._format([])
File "/Users/fengxiaowei/opnfv/releng/utils/test/testapi/venv/lib/python2.7/site-packages/opnfv_testapi/resources/models.py", line 37, in _format
hs.append(h.format())
AttributeError: 'dict' object has no attribute 'format'

JIRA: FUNCTEST-676

Change-Id: I9d8d8a31e5580be51fb690628a03d452742f12d4
Signed-off-by: SerenaFeng <feng.xiaowei@zte.com.cn>