test_interest_loop: no longer passes when commands fail

refs #2386

Change-Id: I71deb55f3655ef7dba11e6532e91ee34309fa32d
diff --git a/test_interest_loop/add-nexthop.sh b/test_interest_loop/add-nexthop.sh
index 363e84b..26dd4ce 100755
--- a/test_interest_loop/add-nexthop.sh
+++ b/test_interest_loop/add-nexthop.sh
@@ -1,5 +1,5 @@
 #!/usr/bin/env bash
 ipaddr=$1
 strategy=$2
-nfdc add-nexthop ndn:/test-loop udp4://$ipaddr
-nfdc set-strategy ndn:/test-loop $strategy
+nfdc add-nexthop ndn:/test-loop udp4://$ipaddr || exit 1
+nfdc set-strategy ndn:/test-loop $strategy || exit 1