Support specifying all_services for host downtime API

[ananace]

For this change to have effect, it requires the corresponding change in the smart-proxy plugin. Without that change this would be a no-op.

Also, the plugin/tests seem to be broken on Foreman 3, guessing because Puppet has moved out of core and so managed hosts no longer have an environment set by default.

[ekohl]

CI was fixed. Would you mind rebasing?

[ochnerd]

@ekohl would you mind merging this? We need it for https://github.com/theforeman/foreman_monitoring/pull/93 and the corresponding change in the smart-proxy plugin https://github.com/theforeman/smart_proxy_monitoring/pull/33.