Build and cache docker images based on the configurations in testserver.
1. Move the shared Docker files to common/shared/testserver
2. Deploy boot2docker image into VirtualBox via docker-machine commands.
3. Build and tag the docker images by the SHA-1 of server context.
Change-Id: Ic5a588e5cc5e753ec4c4e2e1bc79917bbd03f95d
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
