fix NoSuchOptError raised by glance-scheduler when option is nil

2014-01-20 12:57:36.127 3866 CRITICAL cinder [-] no such option: glance_api_insecure
2014-01-20 12:57:36.127 3866 TRACE cinder Traceback (most recent call last):
2014-01-20 12:57:36.127 3866 TRACE cinder   File "/usr/bin/cinder-scheduler", line 60, in <module>
2014-01-20 12:57:36.127 3866 TRACE cinder     service.wait()
2014-01-20 12:57:36.127 3866 TRACE cinder   File "/usr/lib64/python2.6/site-packages/cinder/service.py", line 614, in wait
2014-01-20 12:57:36.127 3866 TRACE cinder     flag_get = CONF.get(flag, None)
2014-01-20 12:57:36.127 3866 TRACE cinder   File "/usr/lib64/python2.6/_abcoll.py", line 336, in get
2014-01-20 12:57:36.127 3866 TRACE cinder     return self[key]
2014-01-20 12:57:36.127 3866 TRACE cinder   File "/usr/lib64/python2.6/site-packages/oslo/config/cfg.py", line 1652, in __getitem__
2014-01-20 12:57:36.127 3866 TRACE cinder     return self.__getattr__(key)
2014-01-20 12:57:36.127 3866 TRACE cinder   File "/usr/lib64/python2.6/site-packages/oslo/config/cfg.py", line 1648, in __getattr__
2014-01-20 12:57:36.127 3866 TRACE cinder     raise NoSuchOptError(name)
2014-01-20 12:57:36.127 3866 TRACE cinder NoSuchOptError: no such option: glance_api_insecure