Utils: Untie the Environment class from the host system.

It is used e.g. in the RemoteLinux plugin
(via ProjectExplorer::EnvironmentAspect) and should
therefore not assume that it's meant for a host system process.

Change-Id: I9f44f862f133579b65951e43fc1e654c425fd3d7
Reviewed-by: Daniel Teske <daniel.teske@digia.com>