Better error message when filesystem watcher causes a problem (hot-relaod, autobuild, localhost server etc.)

[AhtiAhde]

What happens, is that yarn install command does not download the files, which results in mysterious error message. The unfortunate secondary problem is, that the most popular answer to that problem is running yarn install as a system user (sudo), which is not nice.

Having done this several times myself, I believe that the problem might be related to yarn watcher processes, which I use to run third party systems, such as auto-building, hot reloading and running localhost servers. My hypothesis is, that the watcher processes prevent the yarn process from accessing the file system, when trying to write the files; system user usually has much more file I/O privileges, which might explain why sudo solves the issue for many (#4563).

Sure, the proper answer would be to fix those third party processes for ignoring node_modules, but we do not have access to those projects, and some processes might not be able to run without.

A better error message might be proper, when ENOENT errors arise, which might hint towards watcher processes.

I have regular ubuntu 18.04 build; this problem seems to be so common, that I don't believe yarn version is significant factor here.