[vmutils] Add the function OperatingSystem#setCurrentOS.

This function permits to force the current OS.

Signed-off-by: Stéphane Galland <galland@arakhne.org>
[advanced][attrs] Fixing unit test on the cast from String to InetAddress.

Signed-off-by: Stéphane Galland <galland@arakhne.org>
[core][util] Add the multicollection utility class.

This class is a merging view on collections.

Signed-off-by: Stéphane Galland <galland@arakhne.org>