Update maas3 daily stream url, add maas3-release.

[smoser]

The maas3 daily stream url changed, and these tools were broken
as a result. The bug really resided in the tools direct usage
of the maas images file rather than going through index.sjson.

[smoser]

The failure that this is fixing is below.
The old url was:
http://images.maas.io/ephemeral-v3/daily/streams/v1/com.ubuntu.maas:daily:v3:download.sjson
current is:
http://images.maas.io/ephemeral-v3/daily/streams/v1/com.ubuntu.maas:stable:v3:download.sjson

$ snap list image-status
Name          Version  Rev  Tracking     Publisher  Notes
image-status  0.1      45   latest/edge  smoser     -

$ image-status maas3
Traceback (most recent call last):
  File "/snap/image-status/45/usr/bin/sstream-query", line 147, in <module>
    main()
  File "/snap/image-status/45/usr/bin/sstream-query", line 137, in main
    tmirror.sync(smirror, path)
  File "/snap/image-status/45/usr/lib/python3/dist-packages/simplestreams/mirrors/__init__.py", line 85, in sync
    content, payload = reader.read_json(path)
  File "/snap/image-status/45/usr/lib/python3/dist-packages/simplestreams/mirrors/__init__.py", line 41, in read_json
    with self.source(path) as source:
  File "/snap/image-status/45/usr/lib/python3/dist-packages/simplestreams/contentsource.py", line 74, in __enter__
    self.open()
  File "/snap/image-status/45/usr/lib/python3/dist-packages/simplestreams/contentsource.py", line 131, in open
    self.fd = self._open()
  File "/snap/image-status/45/usr/lib/python3/dist-packages/simplestreams/contentsource.py", line 127, in _open
    raise myerr
OSError: Unable to open http://images.maas.io/ephemeral-v3/daily/streams/v1/com.ubuntu.maas:daily:v3:download.sjson. mirrors=[]

[smoser]

@sparkiegeek thanks for reviewing. Can you verify that I did what you wanted ?

[sparkiegeek]

The candidate image stream is found at http://images.maas.io/ephemeral-v3/candidate/streams/v1/com.ubuntu.maas:candidate:v3:download.sjson

The stable image stream is found at http://images.maas.io/ephemeral-v3/stable/streams/v1/com.ubuntu.maas:stable:v3:download.sjson

daily is redirected to stable, so there is no difference between them; but candidate represents what daily used to cover

I tried to suggest the fix to use candidate, but that's not what you picked up :/

[smoser]

The candidate image stream is found at http://images.maas.io/ephemeral-v3/candidate/streams/v1/com.ubuntu.maas:candidate:v3:download.sjson

The stable image stream is found at http://images.maas.io/ephemeral-v3/stable/streams/v1/com.ubuntu.maas:stable:v3:download.sjson

daily is redirected to stable, so there is no difference between them; but candidate represents what daily used to cover

I tried to suggest the fix to use candidate, but that's not what you picked up :/

i think what i did was fail to commit what was in my local tree.

@sparkiegeek, This looks better now?