[merged] status: Support --json option

[cgwalters]

It's really simple to reflect the DBus API into JSON, which tools like
Ansible or jq from the command line or whatever can parse to find
interesting things like the current version.

Closes: #301

[cgwalters]

Things like:

https://github.com/projectatomic/atomic-host-tests/blob/master/tests/upgrade-interrupt/main.yaml#L65

will need to be ported to see if --json exists, if it does, use it, if not fall back.

[miabbott]

Thanks for pointing that out. Happy to see machine readable output for scripting purposes. 😄

[miabbott]

I tested this and saw that some of the field names in the JSON are different from the normal status:

[root@92e55a4fd2da /]# /usr/bin/rpm-ostree status --json | python -m json.tool
[
    {
        "checksum": "4bf265cf86242caa56e86808b1d802034086644aaf75c11b4ef9dbb19d10a5a6",
        "id": "rhel-atomic-host-4bf265cf86242caa56e86808b1d802034086644aaf75c11b4ef9dbb19d10a5a6.0",
        "origin": "rhel-atomic-host-ostree:rhel-atomic-host/7/x86_64/standard",
        "osname": "rhel-atomic-host",
        "serial": 0,
        "timestamp": 1465236727,
        "version": "7.2.5"
    }
]
[root@92e55a4fd2da /]# /usr/bin/rpm-ostree status                             
* rhel-atomic-host-ostree:rhel-atomic-host/7/x86_64/standard
       Version: 7.2.5 (2016-06-06 18:12:07)
        Commit: 4bf265cf86242caa56e86808b1d802034086644aaf75c11b4ef9dbb19d10a5a6
        OSName: rhel-atomic-host
  GPGSignature: (unsigned)

Would it be possible to have the names of the fields be the same in both cases?

[cgwalters]

I know it would be nice if they matched...but we can't change the DBus API since Cockpit uses it (plus various internal consumers).

Trying to align them just for --json would require another reverse mapping table and make this patch much bigger and harder to maintain long term.

We can easily change some of the status nouns like using Checksum: instead of Commit: but...I dunno we don't have a lot of consistency here =/

[miabbott]

I'm in favor of easier maintenance, so the explanation suits me fine.

[jlebon]

Awesome, quite surprising how easy it is.
@rh-atomic-bot r+ 55a81e3

[rh-atomic-bot]

⌛ Testing commit 55a81e3 with merge b7d1b82...

[rh-atomic-bot]

☀️ Test successful - status-atomicjenkins
Approved by: jlebon
Pushing b7d1b82 to master...