Skip xmlrpc discovery when jetpack ready

[malinajirka]

This PR builds on top of #67. When a site responds with "jetpack connected and active" the app knows that Jetpack connection is working without issues and it can skip the xml-rpc check. This should fix an issue discovered by @designsimply

https://wordpress.org/plugins/disable-xml-rpc-api/
When I tried to use the store address > site credentials flow to log in while this plugin is enabled, the error incorrectly tells me that the site at my address is not a valid WordPress site.

To test in WCAndroid:

1. Install "disable-xml-rpc-api plugin
2. Go into its settings and make sure Jetpack is whitelisted
3. Open "Site address" login flow
4. Enter url of the site
5. Make sure it redirects you to the ".com" login and does NOT display "Not a wordpress site" error

[shiki]

@malinajirka Good find! This is fine enough with me. Thanks for fixing it. I found a couple of scenarios that you may be interested in but I'm leaving it to you to decide whether we should still spend more time on this.

Feel free to merge whenever you're ready. 🙂

Before	After

[malinajirka]

Thanks so much for the review @shiki and also for testing extra scenarios to make sure the login flow works as expected!! I wasn't able to reproduce the issues, let me know if you have any tips on how to reproduce them. Thanks!