tests: Stop using ostree trivial-httpd

[cgwalters]

I'm trying to add a libcurl backend to ostree, and I'd like people to stop using
trivial-httpd; it was a mistake to have it be command line API.

Related: ostreedev/ostree#636

(Note I didn't test this commit)

[petervo]

I think we'd be better off just hard coding the port. We know what's running in these test machines to avoid conflicts. The reason for not doing that before was that trivial httpd didn't support the port option on all versions.

Also we probably want to make sure we stop the process.

@cgwalters, if you'd rather not modify this PR, I'm working on some ostree test changes now and I can just incorporate this in with them.

[cgwalters]

Sure, that sounds fine. Regarding stopping, we could pick up the PDEATHSIG code from toolbox maybe.

[stefwalter]

Tests are failing with:

Traceback (most recent call last):
  File "/var/lib/testvm/atomic.install", line 280, in <module>
    cockpit_installer.run()
  File "/var/lib/testvm/atomic.install", line 256, in run
    self.switch_to_local_tree()
  File "/var/lib/testvm/atomic.install", line 89, in switch_to_local_tree
    m = re.search(pattern, webserver_status)

[petervo]

Yeah I'm reworking this. We have to make the script actually run properly. I'll open a pr soon.