[VOL-2049] Disable/Enable ONU Tests

Change-Id: I9db9aab49fd5bb1cddb0245d397c868d18a8e1cf
diff --git a/libraries/voltctl.robot b/libraries/voltctl.robot
index 1dc4f53..5c99633 100644
--- a/libraries/voltctl.robot
+++ b/libraries/voltctl.robot
@@ -50,6 +50,12 @@
     ${rc}    ${output}=    Run and Return Rc and Output    ${VOLTCTL_CONFIG}; voltctl device enable ${device_id}
     Should Be Equal As Integers    ${rc}    0
 
+Disable Device
+    [Arguments]    ${device_id}
+    [Documentation]    Enables a device in VOLTHA
+    ${rc}    ${output}=    Run and Return Rc and Output    ${VOLTCTL_CONFIG}; voltctl device disable ${device_id}
+    Should Be Equal As Integers    ${rc}    0
+
 Get Device Flows from Voltha
     [Arguments]    ${device_id}
     [Documentation]    Gets device flows from VOLTHA