Add an API for VMs to announce support for non-service features. This is
very similar to supported-service.* features, but applies to non-service
features. This may be also used for announcing support for features that
do not use qvm-features framework itself - for example some VM kernel
features, installed drivers, packages etc.
QubesOS/qubes-issues#6030
- Two new methods: .features.check_with_adminvm() and
.check_with_template_and_adminvm(). Common code refactored.
- Two new AdminAPI calls to take advantage of the methods:
- admin.vm.feature.CheckWithAdminVM
- admin.vm.feature.CheckWithTemplateAndAdminVM
- Features manager moved to separate module in anticipation of features
on app object in R5.0. The attribute Features.vm renamed to
Features.subject.
- Documentation, tests.
