[BUG] npm module __virtual__ takes 3 minutes to run when behind corporate firewall/proxy

Description
When the npm.py module loads via __virtual__, it executes the npm --version command:

https://github.com/saltstack/salt/blob/2d17209cafe51fdd00e4f6977fe8771385334ad3/salt/modules/npm.py#L39-L51

Per this bug (and my empirical experience) that command will take 3 minutes to run when behind a corporate firewall that prevents the "update notifier" from connecting to whatever web servers.

Because it's called from inside of the __virtual__, this causes any command that loads all of the modules (i.e. even an unrelated-to-NPM salt-call) to take 3+ minutes to run (and eventually timeout inside the update notifier).

The simplest fix would be to add the env var NO_UPDATE_NOTIFIER=1 to _check_valid_version's cmdmod.run call. I recognize that there are other npm commands inside of npm.py that will run into the same problem, but I'm particularly interested here because this behavior inside of a __virtual__ method is especially problematic due to running at module-load-time even if you don't use any of the NPM module features of Salt (since it's activated by virtue of just having an 'npm' executable found). There is supposedly a command line argument `--no-update-notifier' but I've seen reports online of it not working and have only confirmed that the environment variable fixes the problem.

I've included a version report but this behavior is seemingly common across all platforms.

Versions Report

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