[VOL-4468] Verify that there should be no multicast stream on sending IGMP leave packets

[VOL-4476] Verify that 2 RG which are connected to the different ONU on the same PON Port could join the same channel.

[VOL-4477] Verify that 2 RG which are connected to the different ONU on the same PON Port could join the different channels.

Change-Id: I8b196a3b0d912f96ca5c37c0e0bd9980d114487e
diff --git a/libraries/utils.robot b/libraries/utils.robot
index a6345a9..c7f673d 100755
--- a/libraries/utils.robot
+++ b/libraries/utils.robot
@@ -1255,6 +1255,12 @@
     Run Keyword If    ${value_1} < ${value_2}
     ...    Fail    The value ${value_1} is not larger than or equal to ${value_2}
 
+Should Be Lower Than
+    [Documentation]    Verify that value_1 is < value_2
+    [Arguments]    ${value_1}    ${value_2}
+    Run Keyword If    ${value_1} >= ${value_2}
+    ...    Fail    The value ${value_1} is not lower than ${value_2}
+
 Should Be Float
     [Documentation]    Verify that value is a floating point number type
     [Arguments]    ${value}