GitLab

The error module is not a part of psutil's API and it has been moved
to _error in recent releases. The exceptions in psutil are supposed to
be accessed directly from the top level module.

BUG=406396
R=frankf@chromium.org

Review URL: https://codereview.chromium.org/497763002

Cr-Commit-Position: refs/heads/master@{#300724}