Implement a json formatter in cliff

This change replaces the cliff-tablib json formatter with an internal
replacement. It differs from the tablib formatter in the following ways:
- by default outputs with an indent of 2 spaces. The --noindent formatting
  argument outputs with no indentation, to save space or to pipe to tools
  which can't handle multi-line input.
- emit_one serialises a simple dict where the column name is the key
and the data item is the value (rather than a list of dicts with
'Field' and 'Value' keys)

The cliff release which contains this change will need a corresponding
cliff-tablib release which removes the json formatter from its setup.py
entry_points.

Change-Id: I7f9b1f339d96ead347a0c9d95ec7004a78d8c9d5
Related-Bug: #1308744

cliff/tests/test_formatters_json.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python
+from six import StringIO
+import json
+
+from cliff.formatters import json_format
+
+import mock
+
+
+def test_json_format_one():
+    sf = json_format.JSONFormatter()
+    c = ('a', 'b', 'c', 'd')
+    d = ('A', 'B', 'C', '"escape me"')
+    expected = {
+        'a': 'A',
+        'b': 'B',
+        'c': 'C',
+        'd': '"escape me"'
+    }
+    args = mock.Mock()
+    sf.add_argument_group(args)
+
+    args.noindent = True
+    output = StringIO()
+    sf.emit_one(c, d, output, args)
+    value = output.getvalue()
+    print(len(value.splitlines()))
+    assert 1 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+    args.noindent = False
+    output = StringIO()
+    sf.emit_one(c, d, output, args)
+    value = output.getvalue()
+    assert 6 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+
+def test_json_format_list():
+    sf = json_format.JSONFormatter()
+    c = ('a', 'b', 'c')
+    d = (
+        ('A1', 'B1', 'C1'),
+        ('A2', 'B2', 'C2'),
+        ('A3', 'B3', 'C3')
+    )
+    expected = [
+        {'a': 'A1', 'b': 'B1', 'c': 'C1'},
+        {'a': 'A2', 'b': 'B2', 'c': 'C2'},
+        {'a': 'A3', 'b': 'B3', 'c': 'C3'}
+    ]
+    args = mock.Mock()
+    sf.add_argument_group(args)
+
+    args.noindent = True
+    output = StringIO()
+    sf.emit_list(c, d, output, args)
+    value = output.getvalue()
+    assert 1 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual
+
+    args.noindent = False
+    output = StringIO()
+    sf.emit_list(c, d, output, args)
+    value = output.getvalue()
+    assert 17 == len(value.splitlines())
+    actual = json.loads(value)
+    assert expected == actual