import lib/oslo so we can clean it up

we were calling cleanup_oslo, however we weren't importing
lib/oslo, so that was just throwing an error message and moving on.

Let's stop doing that and actually clean up oslo.

Change-Id: I48340a8b3d5b50477fb5a7e2ce0bed27deb3ec01
diff --git a/clean.sh b/clean.sh
index a443ac8..6ceb5a4 100755
--- a/clean.sh
+++ b/clean.sh
@@ -33,6 +33,7 @@
 source $TOP_DIR/lib/database
 source $TOP_DIR/lib/rpc_backend
 
+source $TOP_DIR/lib/oslo
 source $TOP_DIR/lib/tls
 source $TOP_DIR/lib/horizon
 source $TOP_DIR/lib/keystone