tests: admin_users: make sure repo group is deleted test_delete_repo_group_err creates then deletes a repository group. However, if the delete fails the repository group remains. This later causes problems in the model tests. Introduce a pytest yield fixture to handle the creation _and_ deletion of the repository group (suggested by Søren Løvborg). The creation of the user needs to happen _before_ that of the user group, and we cannot share data between two pytest fixtures, so the user is created in the fixture as well.

[tox]
minversion = 1.8
envlist = py{26,27}-pytest

[testenv]
setenv =
    PYTHONHASHSEED = 0
deps =
    -r{toxinidir}/dev_requirements.txt
    py26-pytest: unittest2
    python-ldap
    python-pam
commands =
    pytest: py.test {posargs}