implements send job_error_occurred notification

When an ERROR scenario occurs while processing a job, we generally
update the job status and its timeout using worker.client.update_job()
method. But currently there is no notifications sent for the error
occurred.
This patch includes the sending of ERROR notification along
with updating of job status as similar to other job processing
notifications.
implementation includes:
- introduce a snapshot._job_error_occurred() to update the job status
  and send appropriate notification on ERROR
- modify worker.process_job() exception handling logic to update the job
  status and send job ERROR notification
- include the error message as part of the notification payload
- add more/modify tests for testing send error notification impl.
implements qonos.job.failed notification

- qonos.job.failed notification is sent only if the following criteria
  is satisfied.
  - If the job status is updated to CANCELLED
    OR
  - If the job status is updated to ERROR (AND)
    if the number of retries exceeds the max retry count (OR) if the
     current time exceeds the  hard_timeout.
- qonos.job.failed notification includes the error message to the job
  payload if it is available while updating the job status.
- modified existing tests to test the send qonos.job.failed notification
  scenario.
Merge pull request #305 from venkateshsampath/qonos_job_failed_notification

implements qonos.job.failed notification
Merge pull request #304 from venkateshsampath/job_error_occurred_notification

implements send job_error_occurred notification
Poll Glance directly for image information

There is really no need for the calls to get image status and
image list and deleting images to go thru Nova. This change allows
Qonos snapshot worker to directly talk to Glance. This also has
the benefits that polling can be done with service admin credentials
thus helping deal with token expirations and getting the image list
can be more tightly filtered with a much smaller list of images
being fetched (i.e. only images created by the scheduled images
service for the specified instance.)

Note that a few tests were deleted. With the change to using
glance the list filtering will happen in on the glance side, not
in the snapshot processor. The deleted tests were effectively
testing that filtering which has been removed.

Fixes to allow http or https for communication