Remove buck.zip from cache on SHA failure

Change-Id: I145c343052729f6a1f1f55cc139506c30113e326
diff --git a/tools/build/onos-buck b/tools/build/onos-buck
index 1a5fd3e..81d3e70 100755
--- a/tools/build/onos-buck
+++ b/tools/build/onos-buck
@@ -27,7 +27,7 @@
         SHA=$(shasum cache/$BUCK_FILE | cut -d' ' -f1)
         [ "$SHA" != "$BUCK_SHA" ] &&
            echo "ERROR: Downloaded SHA ($SHA) does not match expected SHA ($BUCK_SHA)" &&
-           exit 1
+           rm -f cache/$BUCK_FILE && exit 1
     else
         echo "SHA cannot be verified"
     fi