[VOL-3999] Restarting port-forward after restarting VOLTHA-core
component
 Adding explicit error messages for ONOS App upgrade test

Change-Id: I80a2c56dfd26d88d2494d89c67990eb4697fd55c
diff --git a/libraries/voltctl.robot b/libraries/voltctl.robot
index a2b7d8f..73015c7 100755
--- a/libraries/voltctl.robot
+++ b/libraries/voltctl.robot
@@ -650,7 +650,8 @@
     [Documentation]    Gets the device id by matching for ${serial_number}
     ${rc}    ${id}=    Run and Return Rc and Output
     ...    voltctl -c ${VOLTCTL_CONFIG} device list --filter=SerialNumber=${serial_number} --format='{{.Id}}'
-    Should Be Equal As Integers    ${rc}    0
+    Should Be Equal As Integers    ${rc}    0   "Error while fetching device list from VOLTHA"
+    Should Not Be Equal     ${id}   ${EMPTY}    Cannot find device by Serial Number ${serial_number}
     Log    ${id}
     [Return]    ${id}