test: rely on EAL detection for core list

test: rely on EAL detection for core list

Cores count has a direct impact on the time needed to complete unit
tests.

Currently, the core list used for unit test is enforced to "all cores on
the system" with no way for (CI) users to adapt it.
On the other hand, EAL default behavior (when no -c/-l option gets passed)
is to start threads on as many cores available in the process cpu
affinity.

Remove logic from meson: users can then select where to run the tests by
either running meson with a custom cpu affinity (using taskset/cpuset
depending on OS) or by passing a --test-args option to meson.

Example:
$ sudo meson test -C build --suite fast-tests -t 3 --test-args "-l 0-3"

Signed-off-by: David Marchand <david.marchand@redhat.com>
Tested-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Aaron Conole <aconole@redhat.com>