PR to handle vm images for create vm scenarios

Changes in the PR include
1. Support for creating virtual machine using vm images.
2. Support for creating docker vm using vm images.
3. Image Show & Delete Image would now delete vm images.
4. Support for A8,A9 role size for create vm.
The idea is that we look up whether the image under question is available as a "VM Image" or as an "OS Image". We're only interested in raising an error in case the image doesn't show up in both the checks. The callback which is invoked when both the parallel functions complete checks for this and raises a `ResourceNotFound` error in that case.