Adding kokoro config for windows

[tmatsuo]

TODOs

• Add other PHP versions
• Make them children of the main kokoro job or a new parent job for windows
• Determine if we need to have a single parent?

[tmatsuo]

Kokoro windows test is passing for the first time :)
https://source.cloud.google.com/results/invocations/7fb3f264-4f86-436b-b568-3b67f424d68f/targets

[tmatsuo]

@jdpedrie

Can you do a sanity check on the logs of the windows tests?

1. visit the resultstore UI
2. Click Invocation Log
3. Copy the resultstore URL for the individual child jobs and visit it, then click Invocation Log

Maybe you can glance the number of skipped tests and see if the number is within your expectation.

BTW, all the tests are passing, but I noticed the kokoro job on linux doesn't notify to this PR. Possibly we'll need to have a single parent. I'm asking the kokoro team if it's an intended behavior.

[jdpedrie]

Looks good to me. Skipped tests are inline with what we saw on appveyor.

[tmatsuo]

I separated the notification message for the child jobs. We can just ignore the notifications titled child job for now. Kokoro team is working on to disable notifications from child jobs.

[tmatsuo]

@jdpedrie Alright, I think it's ready for review and merge. Can you take a look?

[tmatsuo]

Thanks!