Feat/add missing toggles

[maigl]

This allows to configure 2 (missing) toggles in this provider.

The functionality of both toggles is already implemented in the common provider, only the configuration part was missing in this provider.

Worth noting:

• I tried to add both toggles similar to the openstack provider, unfortunately the naming of disable_updates is not consistent. In the extracspecs it's disable_updates but in the config (and in the code) it's disable_updates_on_boot. Anyway, this mixup is now exactly as it is in the garm-provider-openstack.
• Unlike in garm-provider-openstack, we here have a number of toggles that can only be set via extraspecs but not via config .. this awkward and probably needs to be fixed in future?

Also I sneaked in a commit that allows longer hostnames for linux VMs.

[gabriel-samfira]

Yep. We need to fix that inconsistency. There are also some extra specs in common that should be embeded in most providers (i think all).