adding missing robot library

Change-Id: I2e4188604907f4a8f0e71b58a826b8caa30ad0df
diff --git a/tests/atests/robot/voltha_automated_test_suite.robot b/tests/atests/robot/voltha_automated_test_suite.robot
index 9e764a1..0ac9ae4 100755
--- a/tests/atests/robot/voltha_automated_test_suite.robot
+++ b/tests/atests/robot/voltha_automated_test_suite.robot
@@ -14,6 +14,7 @@
 
 *** Settings ***
 Library           Process
+Library           OperatingSystem
 Library           ../common/auto_test.py
 Library           ../common/volthaMngr.py
 Library           ../common/preprovisioning.py