test/event: add null dev creation in Rx adapter autotest
test/event: add null dev creation in Rx adapter autotest

Allows creation of net_null if vdev EAL option is not specified and
uninit vdev created in the test. The change also adds error checks
for vdev init and uninit.

Signed-off-by: Jay Jayatheerthan <e5f685e50bf6c7e14cabc0fff57c0d810ddf673f@intel.com>
Reviewed-by: Nikhil Rao <d1996eefd6f63075256880b1bd8999364b16b5fc@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk