Fixes
[v1.1][GC] Fix StagesStorage ShouldFetch method: perform fresh docker-inspect, do not use cached inspection result from the previous inspect.
This fix particularly needed for the v1.2 host cleanup procedure which can remove freshly built and saved into the stages storage images. In such case should-fetch and stages-storage-manager fetch method will lock an image and perform standard fetch procedure.
[v1.1] Added stage image locking into stages-storage-manager to prevent v1.2 host cleanup procedure from deleting stages which are in use.