Make consumer_for a context manager

This patch converts consumer_for into a `contextmanager` decorated
method and adapts `__getattribute__` to support this change. A new
method was not added to avoid clashes with method names in the stages.

Change-Id: I6c0727e86d9ee8d6bd34c312d180040c8baf34ba
chore: Remove remaining proxy cruft

Finishing up the removal of the deprecated proxy stuff.

Change-Id: I48f2dc3f382bc882b2e006c17438301c6ee92df9
fix: Reduce logging severity of certain errors

Here are the proposed changes:
- OverflowedJsonInteger: exception -> debug
- InvalidJson: exception -> debug
- InvalidQueueName: warning -> debug

Rationale: these pollute the server logs and provide little value to
system operators.

Change-Id: Icd73a5bd3fc7d7ef349b18e7e485df8a7dfc0a1a
Closes-Bug: #1246977
Remove gettext magic and import _ explicitly

Instead of magically loading `_` into python built-in globals, import it
explicitly where needed.

Partially-implements: py3k-support
Change-Id: Icfedf9f86ead81bbee038506a91c456907af0d05
Disable keystone client if running under Py3K

Since keystoneclient is not Py3K compliant, it should be disabled when
running under python >= 2.7

Partially-implements: py3k-support
Change-Id: I9016748b3fc65f1437cb0d561b738ede704f642f
Don't use tuple parameters

Tuple parameters where removed from Py3K.

Partially-implements: py3k-support
Change-Id: Ibc57f5f3b25c240f48f5c1d9e54cd1d8e5972ea3
Use relative import for base in tests

Py3K fails to import base for tests. Use a relative import instead of an
absolute one.

Partially-implements: py3k-support
Change-Id: I3f3ef511c199a38a8e99c578364b80280f673226
Remove the __MARCONI_SETUP_ global from init

This was used to know when Marconi was being loaded and avoid
registering configuration options and doing other things. This is not
necessary anymore.

Change-Id: Icf43302581eefb563b10ddec5831eeec0d068872
Partially-Implements: py3k-support
Merge "fix: Reduce logging severity of certain errors"
Merge "Make consumer_for a context manager"
Merge "chore: Remove remaining proxy cruft"