app/test: remove meson dependency on file in /sys

app/test: remove meson dependency on file in /sys

Meson versions 0.52 and 0.53 are being overly smart and detecting the path
"/sys/devices/system/cpu/present" in the call to cat in
app/test/meson.build and then adding it as a dependency to the build
configuration. This causes issues on systems where the timestamp of that
file always returns the current time, since it means that the build.ninja
file is always out of date, and therefore needs to be rebuilt.

We can fix this by just using a simple shell script to return the coremask
appropriately for BSD and Linux, and removing that code logic from meson -
thereby hiding the use of the /sys file.

Fixes: c70622ac6f72 ("test: detect number of cores with meson")
Cc: stable@dpdk.org
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>