systems: thermal: use redfish error log checking

Symptom:
Auto test got failed from redfish/systems/test_thermal_ambient_temperatures.robot
Error is "Unexpected BMC error log(s) present.: 200 != 404" and result is FAIL
Get Thermal Records and Verify                         | FAIL |
Reboot And Check Ambient Temperature Records Are Valid | FAIL |

Root cause:
In Test Setup that already change to use redfish error log purging.
But, "Get Thermal Records and Verify" still using legacy method
"Error Logs Should Not Exist" then cause unexpected error log present.

Solution:
Using redfish error log checking "Event Log Should Not Exist" instead.

Tested:
Run robot test redfish/systems/test_thermal_ambient_temperatures.robot.
Get Thermal Records and Verify                         | PASS |
Reboot And Check Ambient Temperature Records Are Valid | PASS |

Signed-off-by: Tim Lee <timlee660101@gmail.com>
Change-Id: I6d68001fb04abb989d492cc14198677e4c540132
diff --git a/lib/logging_utils.robot b/lib/logging_utils.robot
index b6eee94..74209ab 100644
--- a/lib/logging_utils.robot
+++ b/lib/logging_utils.robot
@@ -311,3 +311,9 @@
     Redfish.Post  ${target_action}  body={'target': '${target_action}'}
     ...  valid_status_codes=[${HTTP_OK}, ${HTTP_NO_CONTENT}]
 
+
+Event Log Should Not Exist
+    [Documentation]  Event log entries should not exist.
+
+    ${elogs}=  Get Event Logs
+    Should Be Empty  ${elogs}  msg=System event log entry is not empty.