The REST API doesn't suppprt creation, update and deletion of
non-default dashboards. While updates and deletions were rejected with
'405 Method Not Allowed', creations were rejected with '404 Not Found'.
Make this consistent and always fail requests for non-default dashboards
with '405 Method Not Allowed'.
In addition include an error message in these cases.
Signed-off-by: Edwin Kempin <ekempin@google.com>
Change-Id: I414b8070ff4671e5a79ac5561efc70ce96272c9d
52d54f2b4f