Utils: Introduce new class OsSpecificAspects.

This is basically a generalization of HostOsInfo for
a system that might not be the host system. HostOsInfo
is now implemented in terms of the new class.
Prospective use case: Untie Utils::Environment from
the host system.

Change-Id: If333b96674652109fcb0ad79f75aaaf5e86e17e3
Reviewed-by: hjk <hjk121@nokiamail.com>
Reviewed-by: Daniel Teske <daniel.teske@digia.com>