Remove all *.pyc files in $DEST when executing clean.sh

Currentlly, the *.pyc files could not be removed in any scripts or
functions. But the redundant files would lead stack.sh not to find the
correct script for some versions after branch switched from master to
stable/mitaka in migration_helpers.sync_database_to_version.

So this commit adds the process of cleaning all the *.pyc files in
clean.sh.

It is needed to execute clean.sh before re-stack.sh to prevent the
exception.

Change-Id: I9ba0674d6b20b13c0a26b22cd5d1939daa121a94
Closes-Bug: #1599124
diff --git a/clean.sh b/clean.sh
index 0641bff..e0ec9f5 100755
--- a/clean.sh
+++ b/clean.sh
@@ -145,3 +145,8 @@
 done
 
 rm -rf ~/.config/openstack
+
+# Clean up all *.pyc files
+if [[ -n "$DEST" ]] && [[ -d "$DEST" ]]; then
+    sudo find $DEST -name "*.pyc" -print0 | xargs -0 rm
+fi