west: v0.14.0 is required now (and soon, v1.1)

Commit ce2a7d9a
("scripts: zephyr_module: handle expected west errors")
introduced some better error handling that requires
west version v0.14.0 or later to work.

Bump the west version in requirements-base.txt accordingly.

Due to the way zephyr_module.py is handling imports, this API change
resulted in zephyr_module.py running on older versions of west
reacting as if west was not installed, instead of erroring out.
Fix that so users who are on older west will get a hard error.

(We're about to force everyone to move to west v1.1 as soon as I can
get that release done, but this hotfix should still be helpful in the
interim as well.)

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>