add dynamic node attribute for last apply

so we can check if something has changed in the repo since the last
apply

hooks/deploy_commit_hash_to_node.py

@@ -0,0 +1,5 @@
+def node_apply_end(repo, node, duration, interactive, result, **kwargs):
+    if not node.os in node.OS_FAMILY_UNIX:
+        return
+
+    node.run(f'echo "{repo.revision}" > /var/lib/bundlewrap/last_apply_commit_id')