openstack: fix dispatcher

[s-urbaniak]

Currently the dispatcher func always performs fetching from config
drive, but never from a metadata service.

This fixes it.

[s-urbaniak]

This may fix coreos/bugs#1817 actually, if vexxhost provides igniton via the metadata service.

[s-urbaniak]

/cc @alexsomesan

[crawford]

That looks awfully suspicious... Good catch!

[crawford]

Verified that this works with the metadata service:

$ journalctl -t ignition
-- Logs begin at Wed 2017-02-22 01:29:59 UTC, end at Wed 2017-02-22 01:31:22 UTC. --
Feb 22 01:30:01 localhost ignition[365]: Ignition v0.12.1-43-g966c47f-dirty
Feb 22 01:30:01 localhost ignition[365]: parsed url from cmdline: ""
Feb 22 01:30:01 localhost ignition[365]: no config URL provided
Feb 22 01:30:01 localhost ignition[365]: GET http://169.254.169.254/openstack/latest/user_data: attempt #1
Feb 22 01:30:01 localhost ignition[365]: config drive ("/dev/disk/by-label/config-2") not found. Waiting...
Feb 22 01:30:02 localhost ignition[365]: config drive ("/dev/disk/by-label/config-2") not found. Waiting...
Feb 22 01:30:02 localhost ignition[365]: GET result: OK
Feb 22 01:30:02 localhost ignition[423]: Ignition v0.12.1-43-g966c47f-dirty