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Refs #3440

Refs #3440

Refs #3440

All Exceptions that AstakosClient is raising should
be under AstakosClientException class

Refs #3440

Refs #3440

Rename functions/methods according to PEP-8 naming conventions.

* NoDisplayName
  raised if getDisplayName called with non-existing uuid

* NoUUID
  raised if getUUID called with non-existing display_name

* Move retry decorator to utils module.
* Rename exceptions to be more intuitive.
* Add 403 Forbidden exception.
* Move exceptions to errors class

Refs: #3419

* AstakosClientEInvalid:
    Invalid X-Auth-Token, 401
* AstakosClientEMethod:
    Method not allowed, 400
* AstakosClientENotFound:
    Not Found, 404

Log retries.
Log hashed tokens.

Remove token argument from class initialization
method and make it a mandatory argument to all
the other class methods.

Never, ever log tokens

Creating a new function `_doRequest' to handle
the actual requests to astakos service makes
it easy to mock it later for unit testing
our module.

This function will handle all requests to Astakos.
On top of this we should build high level wrapper
functions to handle more specific calls/requests
to Astakos. _callAstakos function should log
every single action.