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.
We have added required environment changes to most of the tests. Some of the tests do not need the required environment change as the values are defined within the tests. Logging an issue in our repo to track this and see if we have missed the requirement environment changes in other tests.
https://github.com/MSOpenTech/azure-sdk-tools-xplat/issues/38