Drop pylint due to the huge amount of false positives

Given that pylint is raising a lot of false positives
and that we have alternative static code checkers,
we decided to remove pylint from the tox envlist.

This patch also fix some pylint true positives
and cleans up the disabled pylint tests in the codebase.

Change-Id: I6fb4b9b4c80af452796032736e39ef064b9bcd03
Closes-Bug: #1297994
Implement POP in v1.1 API

This patch implements the pop functionality for v1.1 of the Marconi
API. The POP functionality is implemented as an optional parameter
in the delete messages using id params endpoint. This includes the
following validations,
1. pop & id params cannot be used together in the request.
2. 0 < pop value <= max_messages_per_claim_or_pop

docImpact
Change-Id: I63b22e57ed5ab398b81cde2d0284767e9704ec11
Implements: blueprint api-v1.1-pop-operation