My Jetpack: check user connectivity before hitting wpcom side

[retrofox]

Fixes #

Changes proposed in this Pull Request:

• My Jetpack: check user connectivity before hitting wpcom side

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• Go to My Jetpack dashboard
• With a user connected, confirm no issues in there
• Disconnect the user

Without these changes,

• App got broken. White screen.

• Confirm you get an error in the client.

• Check the site/purchases endpoint. Get an error without error status:

** With these changes**

• Confirm you see the error in the dev console

• App is not broken. You still see the products list and My Plan section

• You'd like to take a look at the network tab, too.

[github-actions]

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[oskosk]

LGTM. Not sure about the error message: You are not connected to Jetpack as the check we're doing is for the site-level connection. Something like This site is not connected may be better but this can be part of another PR.

[retrofox]

LGTM. Not sure about the error message: You are not connected to Jetpack as the check we're doing is for the site-level connection. Something like This site is not connected may be better but this can be part of another PR.

Oh... too late. Going to update the text. This site is not connected sounds good to me.