oauthclient: error handling and tests

* Add error handling when the exchange of code for access token fails.

* Adds tests to increase test coverage to 97%.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
oauth2server: settings test

* Add simple test of settings view.

* Fixes file header issue and some PEP8 errors.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
oauthclient: helper test case

* Adds test case class to make custom oauthclient testing
  easier.

Signed-off-by: Lars Holm Nielsen <lars.holm.nielsen@cern.ch>
oaiharvest: reliability improvement and docs

* Prints not only error logs for every workflow, but also
  everything with a superior code error (40) like critical.

* Removes useless part of code.

* Adds basic sphinx documentation syntaxes to various functions.

* Reactivates mails and tickets for harvesting process.

Reviewed-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
Signed-off-by: Guillaume Lastecoueres <guillaume.lastecoueres@cern.ch>