[rdo-dev] changing default ansible to 2.8 for rdo zuul jobs

In order to benefit from improved support for detecting python interpreter (rhel8/centos8) we want to update default version of ansible used by zuul to be 2.8 This will happen when we merge: https://review.rdoproject.org/r/#/c/21996/ As this will affect any job running on zuul that does not already have an override please use Depends-On to test that this will not break your jobs. If you have reasons to delay the upgrade there are two options: * fix the bugs * add "ansible-version: 2.7" to the affected job to assure that changing the default will not affect it. We aim to perform the change next Friday, but we will also discuss it in our weekly meetings <https://etherpad.openstack.org/p/RDO-Meeting>;. Now, I should be back to trigger few more test changes to see what are the outcomes. Few days ago we already changed default Ansible used by ovb jobs to 2.8 and it all went well. Thanks Sorin Sbarnea