[VOL-3638] Using of id instead of device serial number to fetch device info

Change-Id: I22613c190ce4f99ffd5a98f5db71512ddc6b9742
diff --git a/tests/functional/Voltha_ScaleFunctionalTests.robot b/tests/functional/Voltha_ScaleFunctionalTests.robot
index 3eb1576..deb6251 100644
--- a/tests/functional/Voltha_ScaleFunctionalTests.robot
+++ b/tests/functional/Voltha_ScaleFunctionalTests.robot
@@ -123,8 +123,9 @@
     #validate total number of DHCP allocations
     FOR    ${I}    IN RANGE    0    ${num_olts}
         ${olt_serial_number}=    Set Variable    ${list_olts}[${I}][sn]
+        ${of_id}=    Wait Until Keyword Succeeds    60s    5s    Validate OLT Device in ONOS    ${olt_serial_number}
         Wait Until Keyword Succeeds  ${long_timeout}  20s  Validate DHCP Allocations  ${onos_ssh_connection}
-        ...    16   ${olt_serial_number}    BBSM
+        ...    16   ${of_id}    BBSM
     END
     #validate DHCP allocation for each port
     FOR    ${I}    IN RANGE    0    ${num_onus}