app/pdump: exit with primary process

app/pdump: exit with primary process

The pdump tool works as the secondary process. When the primary process
exits and the residual secondary process keeps running, it will make the
primary process can't start up again. Since the ex-fbarry files are still
attached by the secondary process pdump, the 'new' primary process can't
get these files locked.

The patch is to set up an alarm which runs every 0.5s periodically
to monitor the primary process in the pdump. Once the primary exits,
so will the pdump.

Signed-off-by: Suanming Mou <mousuanming@huawei.com>
Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>
Acked-by: Reshma Pattan <reshma.pattan@intel.com>