ssh: fix flakey ssh errors on BSD systems

There's been a persistent issue with flakiness on BSD systems (like OSX) where
the 'no suitable response from remote hg' message would sometimes not appear.
This was caused by one of the earlier calls failing with a "IOError: Broken
pipe". Catching those errors and printing the same message removes the
flakiness.

Differential Revision: https://phab.mercurial-scm.org/D687

mercurial/sshpeer.py

@@ -203,12 +203,21 b' class sshpeer(wireproto.wirepeer):'
         self._pipei = doublepipe(self.ui, self._pipei, self._pipee)
         self._pipeo = doublepipe(self.ui, self._pipeo, self._pipee)
 
+        def badresponse():
+            self._abort(error.RepoError(_('no suitable response from '
+                                          'remote hg')))
+
+        try:
         # skip any noise generated by remote shell
         self._callstream("hello")
         r = self._callstream("between", pairs=("%s-%s" % ("0"*40, "0"*40)))
+        except IOError:
+            badresponse()
+
         lines = ["", "dummy"]
         max_noise = 500
         while lines[-1] and max_noise:
+            try:
             l = r.readline()
             self._readerr()
             if lines[-1] == "1\n" and l == "\n":
@@ -217,9 +226,10 b' class sshpeer(wireproto.wirepeer):'
                 self.ui.debug("remote: ", l)
             lines.append(l)
             max_noise -= 1
+            except IOError:
+                badresponse()
         else:
-            self._abort(error.RepoError(_('no suitable response from '
-                                          'remote hg')))
+            badresponse()
 
         self._caps = set()
         for l in reversed(lines):