* ansible: upgrade to version >= 2.15.5

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

* tests: update requirements

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

* contrib/openstack: fix wrong gitignore pattern

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

* tests: add missing tzdata requirement

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

* tests: remove some molecules tests

Those doesn't work in Ansible 2.15. Ansible can't load builtin now
apparently and these tests are not worth it.

Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>

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Signed-off-by: Arthur Outhenin-Chalandre <arthur@cri.epita.fr>