capsicum-test: Update for O_BENEATH removal

capsicum-test: Update for O_BENEATH removal

Update the tests to check O_RESOLVE_BENEATH instead.
If this looks reasonable, I'll try to upstream this change.
This keeps a compat fallback for O_BENEATH since the Linux port still
has/had O_BENEATH with "no .., no absolute paths" semantics.

Test Plan:	`/usr/tests/sys/capsicum/capsicum-test -u 977` passes and
		runs the O_RESOLVE_BENEATH tests.
Reviewed By:	markj
Differential Revision: https://reviews.freebsd.org/D29016

(cherry picked from commit 8cf5812af4b7f4933983822ff8e1e9185818fbef)