Handle a list of strings from a dict in text output

This situation comes up in commands such as
`aws ec2 describe-load-balancers`.  The output
now looks as expected:

Now:
AVAILABILITYZONES	us-west-2a
HEALTHCHECK	10	30	HTTP:80/index.html	5	2
LISTENER	80	HTTP	80	HTTP
SOURCESECURITYGROUP	amazon-elb-sg	amazon-elb
LOADBALANCERDESCRIPTIONS		a	b	c	d
AVAILABILITYZONES	us-west-2b

Before:

AVAILABILITYZONES	us-west-2a
HEALTHCHECK	10	30	HTTP:80/index.html	5	2
LISTENER	80	HTTP	80	HTTP
SOURCESECURITYGROUP	amazon-elb-sg	amazon-elb
LOADBALANCERDESCRIPTIONS		a	b	c	d
us-west-2b

awscli/text.py

@@ -41,6 +41,10 @@ def _format_text(item, stream, identifier=None, scalar_keys=None):
                 for list_element in item:
                     _format_text(list_element, stream=stream,
                                  identifier=identifier)
+            elif identifier is not None:
+                for list_element in item:
+                    stream.write('%s\t%s\n' % (identifier.upper(),
+                                               list_element))
             else:
                 # For a bare list, just print the contents.
                 stream.write('\t'.join([six.text_type(el) for el in item]))

tests/unit/test_text.py

@@ -131,6 +131,13 @@ def test_empty_list_mock_calls(self):
         # We should not call .write() at all for an empty list.
         self.assertFalse(fake_stream.write.called)
 
+    def test_list_of_strings_in_dict(self):
+        self.assert_text_renders_to(
+            {"KeyName": ['a', 'b', 'c']},
+            'KEYNAME\ta\n'
+            'KEYNAME\tb\n'
+            'KEYNAME\tc\n')
+
 
 if __name__ == '__main__':
     unittest.main()