test: detect number of cores with meson

test: detect number of cores with meson

The arguments being passed will cause failures on laptops that have,
for instance, 2 cores only.  Most of the tests don't require more
than a single core.  Some require multiple cores (but those tests
should be modified to 'SKIP' when the correct number of cores
aren't available).

The unit test results shouldn't be impacted by this change, but it
allows for a future enhancement to pass flags such as '--no-huge'.

Also include a fix to a reported issue with running on FreeBSD.

Signed-off-by: Aaron Conole <aconole@redhat.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>