main: use - instead of _ for seccomp policy argument
main: use - instead of _ for seccomp policy argument

The other options all user hyphens.

Change-Id: I7f0ab307fd5e50deea8c276bc7a73e43cf692195
Signed-off-by: Dylan Reid <c791bfe44996c1eed9c7149a0c5f12a86d58eb85@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/696714
Reviewed-by: Stephen Barber <7719587e4b5a49340661b214ec85602f3918d06f@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm