Ignore status message for HTTP/2

[genki]

To avoid setting status message that is not supported by HTTP/2, checked if the request's HTTP major version is less than 2.
Without this fix some of apps using this package shows warning as follows

(node:49588) UnsupportedWarning: Status message is not supported by HTTP/2 (RFC7540 8.1.2.4)

[genki]

I found that in node 9.x an unexpected warning (as follows) had caught and failed the test.

(node:2676) ExperimentalWarning: The http2 module is an experimental API.

So I fixed the test to recognize the type of warning.

[genki]

@dougwilson Would you mind if I ask you to proceed the workflow?
I have completed to add the test and confirmed it gets succeeded in several environments.

[dougwilson]

Thanks! Sorry it was a holiday weekend. I'm not sure this module actually works with http2 yet, though, but landing this would imply it does. I'll need to check that out before we can land, to make sure http2 even works right. I wouldn't want people thinking it does with this and ending up with some kind of dos vector. Need to make sure the features all work and this module behaves correctly when it encounters broken pipes, half written reaponses, etc

[genki]

I am looking forward to have done it :)