STC changes to make smoke test more reliable

Change-Id: I8ecf2581b12e618bf3fe41baedf5c5decdd77221
diff --git a/tools/test/scenarios/net-link-down-up.xml b/tools/test/scenarios/net-link-down-up.xml
index 8bcbfa7..eb4727b 100644
--- a/tools/test/scenarios/net-link-down-up.xml
+++ b/tools/test/scenarios/net-link-down-up.xml
@@ -20,7 +20,9 @@
               exec="onos-mininet sendAndExpect h1 ping -c1 h4 --expect \ 0% packet loss"/>
         <step name="Link-1-Down" requires="~Ping-1"
               exec="onos-mininet sendAndExpect link s4 s7 down --expect ."/>
-        <step name="Ping-2" requires="~Link-1-Down"
+        <step name="Ping-2-Prep" requires="~Link-1-Down"
+              exec="onos-mininet sendAndExpect h1 ping -c5 h4 --expect ."/>
+        <step name="Ping-2" requires="~Ping-2-Prep"
               exec="onos-mininet sendAndExpect h1 ping -c1 h4 --expect \ 0% packet loss"/>
         <step name="Link-2-Down" requires="~Ping-2"
               exec="onos-mininet sendAndExpect link s4 s5 down --expect ."/>
@@ -28,11 +30,15 @@
               exec="onos-mininet sendAndExpect h1 ping -c1 -w1 h4 --expect 100% packet loss"/>
         <step name="Link-1-Up" requires="~Ping-3"
               exec="onos-mininet sendAndExpect link s4 s7 up --expect ."/>
-        <step name="Ping-4" requires="~Link-1-Up"
+        <step name="Ping-4-Prep" requires="~Link-1-Up"
+              exec="onos-mininet sendAndExpect h1 ping -c5 h4 --expect ."/>
+        <step name="Ping-4" requires="~Ping-4-Prep"
               exec="onos-mininet sendAndExpect h1 ping -c1 h4 --expect \ 0% packet loss"/>
         <step name="Link-2-Up" requires="~Ping-4"
               exec="onos-mininet sendAndExpect link s4 s5 up --expect ."/>
-        <step name="Ping-5" requires="~Link-2-Up"
+        <step name="Ping-5-Prep" requires="~Link-2-Up"
+              exec="onos-mininet sendAndExpect h1 ping -c5 h4 --expect ."/>
+        <step name="Ping-5" requires="~Ping-5-Prep"
               exec="onos-mininet sendAndExpect h1 ping -c1 h4 --expect \ 0% packet loss"/>
     </group>
-</scenario>
\ No newline at end of file
+</scenario>