Added information about debugging unit test with tox.
Replace 3 references to py26 with py34 to reflect current
rally tox configuration.
Co-Authored-By: Illia Khudoshyn <ikhudoshyn@mirantis.com>
Change-Id: I10c865fae473111b35dca1b9c8f51f31ba066b42
closes-bug: 1547265