Updating onos_stage.py to use ONOS_VERSION global

Also, fixing up the base directory for RC packaging.

Change-Id: Id3c80a75ec27bd887b01a04a3122a2660c8f281b
diff --git a/tools/package/onos-prep-karaf b/tools/package/onos-prep-karaf
index bbb6f0e..0dca061 100755
--- a/tools/package/onos-prep-karaf
+++ b/tools/package/onos-prep-karaf
@@ -12,7 +12,7 @@
 #FIXME karaf version
 KARAF_VERSION="3.0.5"
 
-PREFIX="onos-${ONOS_VERSION/-*/}"
+PREFIX="onos-${ONOS_VERSION/-SNAPSHOT/}"
 
 # Unroll the Apache Karaf bits, prune them and make ONOS top-level directories.
 tar xf $KARAF_TAR