We should install python3-* instead of python2-* in CentOS8.
This change fixes the remaining usage of python2-* left for
netwokring-ansible and networking-baremetal.
This includes 260aa9fe29 which fixed
the wrong package names in unit tests.
(cherry picked from commit 34b5036ed8)
(cherry picked from commit ca26611290)
(cherry picked from commit b85b99dfac)