test/crypto: create unique driver name

Since commit <dda987315ca2> ("vdev: make virtual bus use
its device struct"), rte_eal_vdev_init cannot be called
with same name twice.

If several devices with the same driver are needed
(as in the crypto scheduler test), then driver name argument
has to be unique, concatenating the driver name and an index.

Signed-off-by: Pablo de Lara <pablo.de.lara.guarch@intel.com>
Acked-by: Fan Zhang <roy.fan.zhang@intel.com>