Support cloud-init to configure instances

[simon3z]

Add support for cloud-init. The support will probably have to be implemented in each driver.

[jscotka]

Hi,
now I've solve missing feature via own function virtinstall, where is at the end called function setup_vm (which copy ssh key on guest and run init section over ssh) https://github.com/jscotka/cockpit/blob/new_test_structure/test/tests/lib/create_test_machine.sh#L120
called from
https://github.com/jscotka/cockpit/blob/new_test_structure/test/tests/lib/create_test_machine.sh#L35

Regards
Honza