tests: Remove hard-coded EAL param counts

The 'rte_eal_init' function returns the number of EAL arguments
parsed. Use it.

Change-Id: I39f7f9302d746a0d229126e1fc92e3c8e8000b0a
Signed-off-by: Stephen Finucane <stephen.finucane@intel.com>
Reviewed-by: Kevin Traynor <kevin.traynor@intel.com>
Reviewed-by: Meghan Halton <meghan.halton@intel.com>