Allow docker build to set the git hash based version string

Change-Id: Ia9db74bfcaea9eb1fc91bdfb1941f00a86e7c964
diff --git a/Dockerfile b/Dockerfile
index 51b1a58..a4709b8 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -22,7 +22,7 @@
         mkdir -p /src/tar && \
         cd /src/tar && \
         tar -xf /src/onos/buck-out/gen/tools/package/onos-package/onos.tar.gz --strip-components=1 && \
-        rm -rf /src/onos/buck-out
+        rm -rf /src/onos/buck-out .git
 
 
 # Second stage is the runtime environment