Prefer bootstrapped tools when running certctl.sh

Otherwise we get lots of warnings when building on Linux/macOS during
installworld:
Scanning /local/scratch/alr48/cheri/output/freebsd-x86/usr/share/certs/blacklisted for certificates...
install: invalid option -- 'U'
Try 'install --help' for more information.
install: invalid option -- 'U'
....

Reviewed By: kevans
Differential Revision: https://reviews.freebsd.org/D26481