[Bug] Plugin manager does not connect after any single plugin is installed

[TimMonko]

In a fresh environment and pip install napari[all], plugin manager can only properly install one plugin. After restarting napari (as requested by the informational popup, see #123), each attempt to use the Plugin Manager is met with:
WARNING: Plugin manager: There seems to be an issue with network connectivity. Remote plugins cannot be installed, only local ones.

Accordingly, ability to Update or manage plugin versions is lost as is the ability to search for plugins.

I just discovered that spamming the Refresh button can trigger the ability to search for plugins again, and also restore the ability to update plugins:

Finally, I noticed after #123, but not yet restarting napari, that pressing Refresh made me lose the Update ability, but I closed napari too quickly afterwards. Perhaps the lack of connection occurs even without restarting napari.

EDIT: Once this connection is restored, it appears to never happen again on any restart, even after installing further plugins. However, if the connection is not restored, then restarting napari repeatedly does not fix it.