Fix "string_from_json" keyword

Issue-ID: INT-667

Change-Id: Id2dca2630a705c45f293b1b3edddb00f149ac9d5
Signed-off-by: Mariusz Wagner <mariusz.wagner@nokia.com>
diff --git a/test/csit/tests/common.robot b/test/csit/tests/common.robot
index 8af66a5..f0dea25 100644
--- a/test/csit/tests/common.robot
+++ b/test/csit/tests/common.robot
@@ -1,6 +1,7 @@
 #Robot functions that will be shared also with other tests
 *** Settings ***
 Library     OperatingSystem
+Library     HttpLibrary.HTTP
 
 *** Keywords ***
 json_from_file