Auth errors if getting multiple requests in parallel

[zelima]

originally comes from here datopian/datahub-qa#126

Sometimes pushing the files result in an error from auth service. Usually, re-pushing helps.
Besides this, if you try and push multiple datasets in parallel you might get the same error.

seems like it throws that exception when you hit authz api several times within some short period of time. E.g., I've experienced it while doing multiple "push"s in parallel in the tests - https://travis-ci.org/datahq/data-cli/jobs/344397536#L675

Acceptance Criteria

• we know exact reason why this is happening and fix if possible

Tasks

• reporduce locally
• do analysis

[zelima]

FIXED