New build logic for [AETHER-778], [AETHER-779] and [AETHER-782]

- Introduces 2 different tags for tost and tost-onos image
- Stable tag tracks stable commits; master tag tracks ONOS master and tip of the apps
- Updates README and help
- Deprecates the use of the VERSION file
- Uses actual hash for the docker labels

By default DOCKER_TAG points to stable

Change-Id: I7bdb2177b577065a1f4345248c406dcb41ba52a2
diff --git a/VERSION b/VERSION
index 276823b..661235a 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1,2 @@
+# VERSION file is currently unused
 1.0.2-SNAPSHOT