Add final newline to file formatting

The JSON formatting created by jsoncheck.py omits the file's final
newline. It claims that files with such a newline need reformatting
and removes the final newline in a file when reformatting.

This patch brings jsoncheck.py in line with the rest of the tools
which prefer text files to end with a newline.

Update release notes for pushing out the bug fix.

Closes-Bug: #1403159
Change-Id: I35eab544b183c05b167ce9917d92f0f1f919b745

RELEASE_NOTES.rst

@@ -1,6 +1,11 @@
 Release notes
 =============
 
+0.21.1
+------
+
+* ``jsoncheck``: have formatted JSON files end with a newline (lp:bug 1403159)
+
 0.21
 ----
 

os_doc_tools/jsoncheck.py

@@ -107,7 +107,7 @@ def _parse_json(raw):
 def _format_parsed_json(parsed):
     """Pretty-print JSON file content while retaining key order."""
     return json.dumps(parsed, sort_keys=False, separators=(',', ': '),
-                      indent=4)
+                      indent=4) + "\n"
 
 
 def _process_file(path, formatting=None, verbose=False):