don't allow gethostbyname(gethostname()) failure to crash ipcontroller

In some weird situations, socket.gethostbyname_ex(socket.gethostname())
can fail.  Don't let this error raise, instead assume localhost and warn
in these cases.

IPython/parallel/apps/ipcontrollerapp.py

@@ -192,7 +192,13 b' class IPControllerApp(BaseParallelApplication):'
             except AssertionError:
                 pass
             else:
-                location = socket.gethostbyname_ex(socket.gethostname())[2][-1]
+                try:
+                    location = socket.gethostbyname_ex(socket.gethostname())[2][-1]
+                except (socket.gaierror, IndexError):
+                    self.log.warn("Could not identify this machine's IP, assuming 127.0.0.1."
+                    " You may need to specify '--location=<external_ip_address>' to help"
+                    " IPython decide when to connect via loopback.")
+                    location = '127.0.0.1'
             cdict['location'] = location
         fname = os.path.join(self.profile_dir.security_dir, fname)
         with open(fname, 'wb') as f:

IPython/parallel/util.py

@@ -166,8 +166,13 b' def disambiguate_ip_address(ip, location=None):'
     """turn multi-ip interfaces '0.0.0.0' and '*' into connectable
     ones, based on the location (default interpretation of location is localhost)."""
     if ip in ('0.0.0.0', '*'):
-        external_ips = socket.gethostbyname_ex(socket.gethostname())[2]
-        if location is None or location in external_ips:
+        try:
+            external_ips = socket.gethostbyname_ex(socket.gethostname())[2]
+        except (socket.gaierror, IndexError):
+            # couldn't identify this machine, assume localhost
+            external_ips = []
+        if location is None or location in external_ips or not external_ips:
+            # If location is unspecified or cannot be determined, assume local
             ip='127.0.0.1'
         elif location:
             return location