I088fc4284e889147ca9a375d4a159264cff53484 tried to slot the python3
install between the 00-dnf-update and before 01-package-installs;
however it also needs to run *after* the RHEL subscription
00-rhel-registration.
Thus a better place for it is 01-00-centos-python3, which will order
it after subscription and package updates, but before any use of
package-installs.
To avoid confusion over naming, move 00-0-dnf-update back to just
00-dnf-update.
Change-Id: Ib7c82895769e4889d47e10c4b37e06a42c053903
