Cleanup Python 3 changes

* Rework BrickException to simplify the code. Revert partially changes
  done to port os-brick to Python 3, without losing Python 3
  compatibility.
* tox.ini: run py34 tests using the commands of the default test
  environent. All os-brick tests now pass on Python 3.4, so testr test
  runner can be used to run tests in parallel, get the test repository,
  etc.
* tox.ini: exchange order of py27 and py34 in envlist: py34 must be
  run first to workaround a testrepository bug (see the note below).
* README: give advices on tox/testrepository issues with python 2/3

Change-Id: If80e01e802079afea3f2ea8051c76afffa47fa03

README.rst

@@ -11,7 +11,15 @@ Features
 * Discovery of volumes being attached to a host for many transport protocols.
 * Removal of volumes from a host.
 
+Hacking
+-------
 
+Hacking on brick requires python-gdbm (for Debian derived distributions),
+Python 2.7 and Python 3.4. A recent tox is required, as is a recent virtualenv
+(13.1.0 or newer).
+
+If "tox -e py34" fails with the error "db type could not be determined", remove
+the .testrepository/ directory and then run "tox -e py34".
 
 For any other imformation, refer to the parent project, Cinder:
   https://github.com/openstack/cinder

os_brick/exception.py

@@ -37,7 +37,6 @@ class BrickException(Exception):
 
     def __init__(self, message=None, **kwargs):
         self.kwargs = kwargs
-        self.kwargs['message'] = message
 
         if 'code' not in self.kwargs:
             try:
@@ -45,11 +44,7 @@ class BrickException(Exception):
             except AttributeError:
                 pass
 
-        for k, v in self.kwargs.items():
-            if isinstance(v, Exception):
-                self.kwargs[k] = six.text_type(v)
-
-        if self._should_format():
+        if not message:
             try:
                 message = self.message % kwargs
 
@@ -73,9 +68,6 @@ class BrickException(Exception):
     def __unicode__(self):
         return six.text_type(self.msg)
 
-    def _should_format(self):
-        return self.kwargs['message'] is None or '%(message)' in self.message
-
 
 class NotFound(BrickException):
     message = _("Resource could not be found.")

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 1.6
-envlist = py27,py34,pep8
+envlist = py34,py27,pep8
 skipsdist = True
 
 [testenv]
@@ -28,19 +28,6 @@ commands = python setup.py testr --coverage --testr-args='{posargs}'
 [testenv:docs]
 commands = python setup.py build_sphinx
 
-[testenv:py34]
-commands =
-  find . -type f -name "*.pyc" -delete
-  python -m testtools.run \
-    os_brick.tests.test_brick \
-    os_brick.tests.test_exception \
-    os_brick.tests.test_utils \
-    os_brick.tests.initiator.test_connector \
-    os_brick.tests.initiator.test_linuxfc \
-    os_brick.tests.initiator.test_linuxrbd \
-    os_brick.tests.initiator.test_linuxscsi
-
-
 [flake8]
 # H803 skipped on purpose per list discussion.
 # E123, E125 skipped as they are invalid PEP-8.