Merge pull request #14 from dirkmueller/master

Fix changelog generation for python-*client packages
refactor get_parent_dir_and_version_from_tarball function

split in two and add tests
add some more comments about plain_version and parsing the %setup field
Don't try to close non-opened tarball.

The finally clause is always executed after try, so in case of
tarfile.ReadError, it's the wrong approach.
Fix flake8 issues
Standardize pip requirements

The convention is requirements.txt and test-requirements.txt (the latter
including the former).
flake8: Ignore E122 continuation line missing indentation or outdented
Fix Pep8 indentation errors

Hanging indents need to be 4 char indented.
Allow ChangeLog parsing to fail

With PBR >= 0.6, the ChangeLog no longer contains the git
commit hashes.