Fix OLT reboot test for DT workflow

Change-Id: Icc70848312127a8d4dde3652b27e874afe982e21
diff --git a/tests/dt-workflow/Voltha_DT_FailureScenarios.robot b/tests/dt-workflow/Voltha_DT_FailureScenarios.robot
index 5e620ad..5056e4e 100644
--- a/tests/dt-workflow/Voltha_DT_FailureScenarios.robot
+++ b/tests/dt-workflow/Voltha_DT_FailureScenarios.robot
@@ -166,6 +166,8 @@
     # Wait for the OLT to come back up
     Run Keyword If    ${has_dataplane}    Wait Until Keyword Succeeds    360s    10s
     ...    Check Remote System Reachability    True    ${olt_ssh_ip}
+    Wait Until Keyword Succeeds    360s    5s    Validate OLT Device    ENABLED    ACTIVE    REACHABLE
+    ...    ${olt_serial_number}
     # Waiting extra time for the ONUs to come up
     Sleep    60s
     Run Keyword And Ignore Error    Collect Logs