Jetpack connect: avoid showing a generic error message

[johnHackworth]

If we are have just authorized a jetpack site, and we reload the page (or just go to the next screen and the go back to the authorization screen), right now we are going to see a "unknown error" message.

This is because we are trying to authorize the site again, and the API is returning an "already authorized" message, which is not controlled so it defaults to the default generic error message.

This PR changes this, so we can show an "already authorized" message:

How to test

1. Go to http://calypso.localhost:3000/jetpack/connect/ and enter an unconnected jetpack site url
2. Wait until your site is connected, by then you should be at http://calypso.localhost:3000/jetpack/connect/authorize
3. Reload the page (or go to the plans page and the click browser's back button). You should see a message telling you tha te site is already connected, not an error message

@roccotripaldi @rickybanister

[rickybanister]

Could we perhaps redirect the user to the next step instead? (or something like that?)

[johnHackworth]

@rickybanister we could do that... but pretty much that will mean that the user could not use the browser back button (also: confusing and infuriating as hell... as least for me as a user, I hate when I'm trying to go back in my browsing history and a site insists in forwarding me to the next step)

[roccotripaldi]

LGTM!

This made me realize that we need to handle cases where people manually go to /jetpack/connect/authorize by typing it into their address bar. We should probably just kick them back to jetpack/connect - I'll handle that in an other PR.

[rickybanister]

@johnHackworth understood. Perhaps then we render a different set of components here or something.

How would someone navigate to here in the first place? Would they have to type in that url?

What about rendering a drake message saying you're already connected?

[johnHackworth]

@rickybanister this is the url where users are redirected to from their wp-admin ...
so for them, it's /jetpack/connect => /jetpack/connect/authorize =>
/plans ... and this PR deals with what happens if they go back from
/plans to /authorize.

I don't think we could render a different set of components since when we
start rendering this page we don't really know if the user is there for the
first time or if they are back from /plans (or have reloaded the page).
What we could do is, once we try to connect the site and we identify the
site as already connected, show a drake message there instead of the auth
screen, maybe

[johnHackworth]

@rickybanister I'm going to merge this one, to avoid the error message, and we can add the drake screen in another PR