scripts: modules: support west group feature

West has introduced support for group tags in:
https://github.com/zephyrproject-rtos/west/pull/454



This means that manifest files might start containing groups.
Zephyr itself only requires west>=0.7.2 where groups are not supported
but other Zephyr based projects might start using the group feature.

When using a west version with group support, then only active projects
will be processed as Zephyr modules.

West versions without group support will consider all projects active.

Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>