handle name resolution errors more gracefully from shell.py

This change will catch socket.gaierror exceptions from shell.py and
return a more friendly message to the user

lib/ansible/module_utils/shell.py

@@ -101,12 +101,15 @@ class Shell(object):
         if not look_for_keys:
             look_for_keys = password is None
 
+        try:
             self.ssh.connect(host, port=port, username=username, password=password,
                         timeout=timeout, look_for_keys=look_for_keys, pkey=pkey,
                         key_filename=key_filename, allow_agent=allow_agent)
 
             self.shell = self.ssh.invoke_shell()
             self.shell.settimeout(timeout)
+        except socket.gaierror:
+            raise ShellError("unable to resolve host name")
 
         if self.kickstart:
             self.shell.sendall("\n")