Logging what chroot we are killing the orphans in

With all the --uniqueexst, --rootdir, --resultdir, etc. options it is
easy to make a mistake, so this info helps to reassure us everything is
OK.

mock/py/mockbuild/util.py

@@ -164,7 +164,7 @@ def orphansKill(rootToKill, manual_forced=False):
 
     When manual_forced==True, the manual kill based on /proc is enforced.
     """
-    getLog().debug("kill orphans")
+    getLog().debug("kill orphans in chroot %s", rootToKill)
     if USE_NSPAWN is False or manual_forced:
         path_cache = {}
         for killsig in [signal.SIGTERM, signal.SIGKILL]: