bisect: use ui out descriptor when calling util.system

mercurial/commands.py

@@ -562,7 +562,7 b' def bisect(ui, repo, rev=None, extra=Non'
         try:
             while changesets:
                 # update state
-                status = util.system(command)
+                status = util.system(command, out=ui.fout)
                 if status == 125:
                     transition = "skip"
                 elif status == 0: