Handle case when create-virtual-mfa-device errors out

This was previously propogating a KeyError and would just
display the error message 'VirtualMFADevice'.  Now
we let the error propogate and print a full error message.

awscli/customizations/iamvirtmfa.py

@@ -81,6 +81,8 @@ def _add_options(self, argument_table, **kwargs):
         argument_table['bootstrap-method'] = self._method
 
     def _save_file(self, parsed, **kwargs):
+        if 'Error' in parsed:
+            return
         method = self._method.value
         outfile = self._outfile.value
         if method in parsed['VirtualMFADevice']:

tests/functional/iam/test_create_virtual_mfa_device.py

@@ -127,3 +127,28 @@ def test_bad_relative_filename(self):
         cmdline += ' --virtual-mfa-device-name fiebaz'
         cmdline += ' --outfile %s --bootstrap-method QRCodePNG' % outfile
         self.assert_params_for_cmd(cmdline, expected_rc=255)
+
+    def test_bad_response(self):
+        # This can happen if you run the create-virtual-mfa-device
+        # command multiple times with the same name.  You'll get
+        # an "already exists" error and we should handle that case
+        # gracefully.
+        self.parsed_response = {
+            'Error': {
+                'Code': 'EntityAlreadyExists',
+                'Message': 'MFADevice entity at the and name already exists.',
+                'Type': 'Sender',
+            },
+            'ResponseMetadata': {
+                'HTTPStatusCode': 409,
+                'RequestId': 'requset-id'}
+        }
+        self.http_response.status_code = 409
+        cmdline = self.prefix
+        cmdline += ' --virtual-mfa-device-name fiebaz'
+        cmdline += ' --outfile foo --bootstrap-method QRCodePNG'
+        # The error message should be in the stderr.
+        self.assert_params_for_cmd(
+            cmdline,
+            stderr_contains=self.parsed_response['Error']['Message'],
+            expected_rc=255)