Converted vPing to leverage the object-oriented SNAPS library.

Converted vPing to leverage the object-oriented SNAPS library.

JIRA: FUNCTEST-577

1. Replaced procedural openstack_utils with the object-oriented SNAPS
   library
2. Tests now clean themselves up.
3. Improved code documentation.
4. Removed dependency on file-based Cirros image and now leveraging the
   download URL.
5. Removed hardcoded location to the testcases.yaml file to leverage
   the value in config_functest.yaml
6. Included optional flavor metadata based on the scenario being tested
7. Included support for multi-part images.
8. Added enhanced support for configurable images. see SNAPS-76

Fixed line length verification problem with the previous submission
Fixed retrieval of external network name to be dynamic.
Changed external network name retrieval to leverage the newly merged
snap_util.get_ext_net_name() function
Added the creation and deletion of flavors.
SNAPS now has the ability to add/remove security groups from running instances.
Changed VMInstance constructor by moving userdata to configuration object.

Change-Id: I0ef5e268eb153d696bb4d9a7533f780e5c603d26
Signed-off-by: spisarski <s.pisarski@cablelabs.com>