dist: don't execute dpdk scripts if not in dpdk mode
dist: don't execute dpdk scripts if not in dpdk mode

The scripts are not liking very much being executed inside docker.
Since we don't really need those variables set outside DPDK scenarios,
just don't set them.

Signed-off-by: Glauber Costa <7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>
Message-Id: <1488823691-9014-1-git-send-email-7ba9037b0dd006f9408bd45b94707becd5cd4e87@scylladb.com>

avikivity/scylla,scylladb/scylla,duarten/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla,scylladb/scylla,avikivity/scylla,duarten/scylla