fix TypeError: module object is not callable

TypeError when running /usr/bin/oschecks-check_cinder_api

Traceback (most recent call last):
  File "/usr/bin/oschecks-check_cinder_api", line 6, in <module>
    from oschecks.cinder import check_cinder_api
  File "/usr/lib/python2.7/site-packages/oschecks/cinder.py", line 66, in <module>
    class Novautils(object):
  File "/usr/lib/python2.7/site-packages/oschecks/cinder.py", line 81, in Novautils
    def totimestamp(dt=None, epoch=datetime(1970, 1, 1)):
TypeError: 'module' object is not callable

Change-Id: I04f9d3db5132335ad413b2f97d5b1b75752ff105