Host services are a way to provide functionality to stages that is
restricted to the host and not directly available in the container,
such as providing input to stages, devices access and mounting.
This commit introduces a `ServiceManager` class that can be used to
start and (automatically) stop host service, as well as a `Service`
base class together with a `ServiceClient` class that be used to
implement host services and communicate with them. Refer to the doc
string of the module for more information.
