Set Software Instance roles directly from aggregate related object.

Use double interaction, called twice: in order to being able to reset role on
removal or set it on setting.

It allows locating workflow.

Rationale: Hosting Subscription workflow changed.

Access to low level methods will be required.

Drop not needed SlaveInstanceStopComputerPartitionInstallation.

Add parameter to useradd specifying that we have daemon (system) user, not normal one.

This does not work yet.