waiting for the OLT to go down in OLT soft reboot tests

Change-Id: I438fca46d2e9096d8cca541d59809ba3082b3a4b
diff --git a/tests/functional/Voltha_FailureScenarios2.robot b/tests/functional/Voltha_FailureScenarios2.robot
index ab21938..1cf802d 100644
--- a/tests/functional/Voltha_FailureScenarios2.robot
+++ b/tests/functional/Voltha_FailureScenarios2.robot
@@ -69,6 +69,9 @@
     Wait Until Keyword Succeeds    ${timeout}    2s    Perform Sanity Test
     # Reboot the OLT using "voltctl device reboot" command
     Reboot Device    ${olt_device_id}
+    # Wait for the OLT to actually go down
+    Wait Until Keyword Succeeds    360s    5s    Validate OLT Device    ENABLED    UNKNOWN    UNREACHABLE
+    ...    ${olt_serial_number}
     #Verify that ping fails
     FOR    ${I}    IN RANGE    0    ${num_onus}
         ${src}=    Set Variable    ${hosts.src[${I}]}