Delay site is "Unreachable" notification from Jetpack while plugins are being "Updated".

Greetings!
#### Steps to reproduce the issue

1. Update a WP/WC plugins that has Jetpack connectivity monitor enabled. You must have at least 3 or more plugins that require "updating". It would be best if performed when WooCommerce Plugin needs updating. My site has a large number of products over 10,000 and several more thousands in images, I am able to reproduce this problem many many times and have experienced my site being unreachable for many years of using WP/WC. Jetpack just puts what I already know in an email :)

#### What I expected
I would expect not to receive a False Positive that my site is unreachable because plugins are updating.

#### What happened instead
I received an email informing me my site was unreachable by Jetpack, when I went to investigate my site was actually up and running well.

In addition to eliminating a false positive for site being Down, Jetpack should monitor when plugins are being updated. Once the updates are completed Jetpack should wait for at least 60 seconds maybe a little more to check for the site being unreachable or not. With good testing of which plugins require more site reset time calculated Jetpack could adjust accordingly.
Cheers, Jim

No files or tests are identified in the issue. Start by locating Jetpack's connectivity monitor and the path that runs during plugin updates, then reproduce the false unreachable alert with multiple updates in progress. Done means updates no longer trigger a false-positive notification while genuine outages still do.

Written by the indexing model from the issue text.