switch to a whitelist of poison-worthy errors

Summary: There are other errnos possible here, like `ENOTDIR` or `ENOFOLLOWSYMLINK`. It's better to switch to a whitelist of errors we know we can't recover from.

Test Plan: `arc unit --everything`

Reviewers: wez

Reviewed By: wez

Differential Revision: https://phabricator.fb.com/D1510893