Better handle 401 errors returned by Nuxeo

Problem is described in SUPINT-955, see https://jira.nuxeo.com/browse/SUPINT-955?focusedCommentId=331268&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-331268.

We need Drive to be resilient to 401 errors, probably by retrying a certain number of times to distinguish a real Unauthorized error (in the case of a revoked token for instance, then the "Invalid credentials" error makes sense) from an illegitimate 401.