eal: restrict cores auto detection

eal: restrict cores auto detection

This patch uses pthread_getaffinity_np() to narrow down used
cores when none of below options is specified:
  * coremask (-c)
  * corelist (-l)
  * and coremap (--lcores)

The purpose of this patch is to leave out these core related options
when DPDK applications are deployed under container env, so that
users do not need decide the core related parameters when developing
applications. Instead, when applications are deployed in containers,
use cpu-set to constrain which cores can be used inside this container
instance. And DPDK application inside containers just rely on this
auto detect mechanism to start polling threads.

Note: previously, some users are using isolated CPUs, which could
be excluded by default. Please add commands like taskset to use
those cores.

Test example:
$ taskset 0xc0000 ./examples/helloworld/build/helloworld -m 1024

Signed-off-by: Jianfeng Tan <jianfeng.tan@intel.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>