qobject: Factor out helper json_pretty_newline()

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20200415083048.14339-3-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[Coding style in moved code tidied up]
1 file changed