Refactoring metadata/base

- Extracted out methods from get_openstack_item for handling version, content and path
- Replaced the if else style route configuration with a route configuration dict
- This will help adding new apis easier and be maintainable

Change-Id: Ie1885c439f3d119032dd1c7c7af070142987ba7f
Partially implements: blueprint metadata-service-callbacks
Merge "Refactoring metadata/base"