Run device-init in different phases of the boot process

[Govinda-Fichtner]

Some of the actions that device-init have to happen in different phases of the boot-process.

For instance setting the hostname should happen as early as possible.
Others actions like for instance loading Docker images from the filesystem have to happen late in the boot process when Docker is already running.

Thus being able to configure different phase of the boot process when actions are run seems to make sense.