Fix errorlog test cases

Fixes:
   - Sorting URL list
   - Replace hard-coded entry index to list indexing
   - With the new FW elog design change, the error log is now
     persistent on BMC reset or restarting the logging service
   - Add keyword to check if errorlog exist

Resolves openbmc/openbmc-test-automation#732

Change-Id: Iafe54824dc0ed4ef88acd8dd327cbc873cd740aa
Signed-off-by: George Keishing <gkeishin@in.ibm.com>
diff --git a/lib/utils.robot b/lib/utils.robot
index 7006eac..d53aac1 100755
--- a/lib/utils.robot
+++ b/lib/utils.robot
@@ -664,6 +664,7 @@
     #              /xyz/openbmc_project/inventory).
 
     ${url_list}=  Read Properties  ${openbmc_url}/list  quiet=${1}
+    Sort List  ${url_list}
     [Return]  ${url_list}
 
 Get Endpoint Paths