Maintain version-based image tarfiles for pre-pull before tests (Refer PR 19)

[ksatchit]

The proposed changes to reduce CI time by making use of pre-pulled images uses a single tar bundle to hold all the test images. While this does help with improving CI time, a better approach would be to maintain the image tars separately and load them individually. Reasons :

• Currently the application specification YAML files use "latest" tag for some images, and other version-based tags for others. It is necessary to identify changes to the images using "version"-based tags using a separate logic on the test harness machine

• With current logic, even on changes to any one application/test image, the whole tar bundle will be re-applied