scripts: west build: propagate verbosity to cmake generator

When run as "west -v build", make sure that the underlying build tool
is run in verbose mode as well (if the generator is known to support
it, which is the case for Unix Makefiles and Ninja based generators).

The per-generator hacks here are needed to support CMake 3.13. If we
move to CMake 3.14 or later, we can just run "cmake --build BUILD -v"
and be done with it.

Signed-off-by: Marti Bolivar <marti.bolivar@nordicsemi.no>