Update test_ro_disk.py (#14150)

Improve test_ro_disk logrotate failed because auth.log missing issue.

#### Why I did it
test case  test_ro_disk failed because following error:
error: stat of /var/log/syslog failed: Bad message
du: cannot access '/var/log/auth.log': Bad message

### How I did it
Improve test_ro_disk logrotate failed because auth.log missing issue.

#### How to verify it
Pass all test case.

### Description for the changelog
Improve test_ro_disk logrotate failed because auth.log missing issue.

tests/tacacs/test_ro_disk.py

@@ -155,6 +155,12 @@ def log_rotate(duthost):
         if "logrotate does not support parallel execution on the same set of logfiles" in e.message:
             # command will failed when log already in rotating
             logger.warning("logrotate command failed: {}".format(e))
+        elif "error: stat of /var/log/auth.log failed: Bad message" in e.message:
+            # command will failed because auth.log missing
+            logger.warning("logrotate command failed: {}".format(e))
+        elif "du: cannot access '/var/log/auth.log': Bad message" in e.message:
+            # command will failed because auth.log missing
+            logger.warning("logrotate command failed: {}".format(e))
         else:
             raise e