fork child process for processing job.

This patch is to enable forking of child process for processing the
given job. The forking of child process can be enabled or disabled using
the qonos worker config param flag, 'fork_child_process'. By default
fork_child_process is disabled ie., set to 'False'.

RM6152
Merge pull request #317 from CrashenX/qonos_worker_fork_proc

fork child process for processing job.
added missing import for qonos exceptions

The import for qonos exceptions was removed in a previous PR and causes
the tests to fail. This PR adds that import line back in.
Merge pull request #320 from CrashenX/missing_exception_import_in_tests

added missing import for qonos exceptions
Fix localization error in exception.py

Fix issue:-
qonos/common/exception.py:31:48: H701  Empty localization string

Also, localizes strings for other exceptions as well.
Merge pull request #319 from komawar/fix-localization-in-exception

Fix localization error in exception.py
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

Responding to review comments. Added some associated tests.