Currently migrate.versioning.api.upgrade() raises KeyError
instead of sqlalchemy-migrate specific exception if migration
script file is not present in migration repository.

Raised migrate.exception.VersionNotFoundError if the specified
migration script does not exist in the repository. Made
VersionNotFoundError exception class as a subclass of KeyError
in order to avoid breaking existing users looking for KeyError.

Related-Bug: #1546441
Change-Id: I0210d56a6e85f03c44cea027f50863faaf050c1d

Python 3.4 unit test is failing because of
DeprecationWarning: Parameters to load are deprecated.
Called .resolve and .require separately on setuptools >= 11.3.

Made provision to call .resolve() method if setuptools >= 10.2
and less than 11.3 else call .load() method.

Change-Id: I5ba80edfbf6b7c8399c66f01d57c91bd02eab274
Closes-Bug: #1586060

On Python 3, some functions like range() don't try to call the __int__()
method to cast an object to integer, but try instead the __index__()
method.

Add an __index__() method to mimick correctly the int type on Python 3.

Change-Id: I8df116d80e201778714a59367600eaef644266ed

The usage function of migrate_repository.py isn't Python 3 compatible,
and this hasn't be caught by unit tests. This patch fixes the function,
so at least the file can be compiled in Py3.

Change-Id: Ib9333e46e7526e82acde573d4b2046b2bf9a7ae0

There are two changes which have to go together to pass the gate
tests:

1. Update pbr and mock requirements from global-requirements

mock 1.2 supports py26 again so make that the minimum version. The
same change is being made in g-r with:

Ic6b9e18eaec9c81bbbbc57129e024904be928e09

Sync up with latest pbr in global-requirements while we're at it.

Closes-Bug: #1474925

2. Fix the importpath module to work with python >= 3.3 where the
__import__ built-in is raising an ImportError on a temporary file
that is added to the system path.

Closes-Bug: #1475339

Change-Id: Ie98938ba75f3983094dd540b7d26a7ec46be4f6e

In order to raise the cap on pbr we need to update
the dependent versions of the flake8 related packages
for the pep8 job since they have capped pbr.

A couple of simple hacking issues are fixed, the rest
are ignored.

Change-Id: Icddb5bf284da7b6463ebcfc7512726149ffe6085