Enable flake8 F841 checking

This check looks to see whether a local variable
is unused. Fixed all of violators of said check.

Change-Id: I6ff349ca8d650ae7d6ebeeb116a1649b0db8f071
xenapi: move StorageError into global exception.py

We have our own exception for StorageErrors, and this is causing some
interesting dependency issues, so seems best to move this exception into
the more usual place.

Change-Id: I4f1f33e95f1050874ef828af9b35b0edbf8f0176
xenapi: remove calls to call_xenapi in volumeops

As part of the move to remove calls to call_xenapi, this removes calls
in volumeops. This makes the later refactoring and test coverage patches
much easier to write.

Change-Id: I384d7d85382551d32122d475768f015e8dfd8769
xenapi: refactor volumeops attach

Refactor the attach code, so its more readable.

At the same time, add some new unit tests to better cover the volume
attach code.

In a later patch we will remove the older mox tests, and dead code that
is now only left in volumeops to keep those old tests running.

Change-Id: Ic50dba5588bb968eca3ac2bf94c3eb719fa2cf6b
Sync oslo network utils

A new function was added to oslo-incubator for setting tcp keepalive
settings, and dependent projects can use it.

Ran update.py in oslo-incubator to copy changed modules into nova.
Removing synced changes for jsonutils because of issues with how
strings are encoded with simplejson that cause some of our unittests
to fail.

Changes are:
network_utils.py (which contains the function we need, others are deps)
edd73c9 Merge "Improve help strings"
fe3389e Improve help strings
8a0f567 Remove str() from LOG.* and exceptions
f61a4e7 Fix python26 compatibility for RFCSysLogHandler
da6d713 Revert setting oslo-incubator logs to INFO
0d18381 Set default log levels for oslo.messaging and oslo-incubator

gettextutils.py
9912e5d Add API for creating translation functions
6cc96d0 Fix test_gettextutils on Python 3

log.py
edd73c9 Merge "Improve help strings"
fe3389e Improve help strings
8a0f567 Remove str() from LOG.* and exceptions
f61a4e7 Fix python26 compatibility for RFCSysLogHandler
da6d713 Revert setting oslo-incubator logs to INFO
0d18381 Set default log levels for oslo.messaging and oslo-incubator

Current HEAD in OSLO:
----------------------------------------------
Merge: 2640847 e433899
Date:   Mon May 5 19:41:28 2014 +0000
Merge "Enable configuring tcp keepalive"
----------------------------------------------

Implements: blueprint configure-tcp-keepalive
Related-Bug: 1314129
Change-Id: Idd04ad4ad9a06ef76941dc5c1be41ac3ac8877a7
Merge "xenapi: move StorageError into global exception.py"
Merge "xenapi: remove calls to call_xenapi in volumeops"
Merge "xenapi: refactor volumeops attach"
Merge "Sync oslo network utils"