Merge lp:~ubuntu-on-ec2/vmbuilder/jenkins_kvm-philroche-eoan-python3-openstackclient into lp:~ubuntu-on-ec2/vmbuilder/jenkins_kvm [a=philroche] [r=davidkrauser,patviafore]

python-openstackclient was dropped after disco

If we want to create or update builder images post disco we need to migrate to python3-openstackclient

MP: https://code.launchpad.net/~ubuntu-on-ec2/vmbuilder/jenkins_kvm-philroche-eoan-python3-openstackclient/+merge/375547