fix unit tests that cause warnings

[surajssd]

There are some unit tests that cause warnings which clutters the unit test output

✔ ~/go/src/github.com/kubernetes-incubator/kompose [master L|✔]
17:36 $ make test-unit
./script/make.sh test-unit
---> Making bundle: test-unit (in .)
?       github.com/kubernetes-incubator/kompose [no test files]
<snip>
       kubernetes_test.go:215: Test case: Convert to Ingress: label set to example.com
=== RUN   TestKomposeConvert
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
time="2016-12-23T17:37:27+05:30" level=warning msg="Ignoring user directive. User to be specified as a UID (numeric)."
<snip>