Replace one-time-login with a sample plugin in the tests

[Nikschavan]

Fixes #301

Replaces the plugin one-time-login with a sample WordPress plugin

[swissspidy]

@schlessera Should this sample plugin live in the wp-cli org so that we can guarantee it exists? In case https://github.com/Nikschavan/test-wordpress-plugin ever gets deleted :-)

[Nikschavan]

I was hoping it would be simpler to fork and get this into wp-cli org? I mentioned in the issue #301 it would be preferable to be in this org.

Maybe anyone with capabilities can create a repo here instead and I can use that links in this PR?

[wojsmol]

We have https://github.com/wp-cli-test/generic-example-plugin or AFAIK we can transfer @Nikschavan to wp-cli-test organisation.

[Nikschavan]

Ahh, I didn't knew about the generic-example-plugin. That should work for this use case as well. I will use that one instead of creating a new one. Thanks @wojsmol :)

[Nikschavan]

I will need one more help from folks who have access to the repo https://github.com/wp-cli-test/generic-example-plugin.

One of the tests will require a release to be created for the plugin generic-exaple-plugin and a ZIP file to be uploaded to the release, Same as the release on one-time-login plugin - https://github.com/danielbachhuber/one-time-login/releases/tag/v0.1.2

[swissspidy]

That'd have to be @schlessera in that case

[schlessera]

@Nikschavan This is done, the repo now has two published releases, each with a separate ZIP as attached asset.