qapi: Format TODO comments more consistently

Consistently put a colon after TODO.  This will make the TODOs stand
out in the documentation we're going to generate.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20170113144135.5150-4-marcandre.lureau@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
[Commit message rewritten]
Signed-off-by: Markus Armbruster <armbru@redhat.com>

qapi-schema.json

@@ -2314,7 +2314,7 @@
 #                     "mac": "52:54:00:12:34:56" } }
 # <- { "return": {} }
 #
-# TODO This command effectively bypasses QAPI completely due to its
+# TODO: This command effectively bypasses QAPI completely due to its
 # "additional arguments" business.  It shouldn't have been added to
 # the schema in this form.  It should be qapified properly, or
 # replaced by a properly qapified command.
@@ -2515,7 +2515,7 @@
 #
 # Additional arguments depend on the type.
 #
-# TODO This command effectively bypasses QAPI completely due to its
+# TODO: This command effectively bypasses QAPI completely due to its
 # "additional arguments" business.  It shouldn't have been added to
 # the schema in this form.  It should be qapified properly, or
 # replaced by a properly qapified command.

qapi/introspect.json

@@ -258,7 +258,7 @@
 #
 # @ret-type: the name of the command's result type.
 #
-# TODO @success-response (currently irrelevant, because it's QGA, not QMP)
+# TODO: @success-response (currently irrelevant, because it's QGA, not QMP)
 #
 # Since: 2.5
 ##