Improve log output for a negative test case

[ashahi1]

Test is expected to fail since it tries to delete a non-existing vsan policy but from the console log its not clear if its an expected failure or its a genuine product issue.

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console output:

Running unit tests in /tmp/vmdk_ops_unittest21044/vsan_policy_test.py...
...ERROR:root:Failed to remove test_policy policy file
Traceback (most recent call last):
  File "/tmp/vmdk_ops_unittest21044/vsan_policy.py", line 209, in delete
    os.remove(policy_path(name))
OSError: [Errno 2] No such file or directory: '/vmfs/volumes/vsan:52fe282b8b5a398c-e41bd80f9e940d46/dockvols/policies/test_policy'
..

[shuklanirdesh82]

Thanks Anup! Changes are merged so closing this now.