brancher: make brancher cleanup safe against other branchers

If another brancher uses the same push repo we need to make
sure we don't overlap on prefixes. Be more careful when
deciding if we own a branch.

Signed-off-by: Jakub Kicinski <[email protected]>

Author: kuba-moo

pw_brancher.py

@@ -290,6 +290,9 @@ def reap_old(config, state, tree, tgt_remote) -> None:
         br = br.strip()
         if not br.startswith(r_tgt_pfx + pfx):
             continue
+        # In case our prefix is a prefix of another brancher
+        if len(br) != len(r_tgt_pfx + pfx + "2000-01-01--00-00"):
+            continue
         br = br[len(r_tgt_pfx):]
         found.add(br)
         if br not in state["branches"]: