Fix DevStack setup on CentOS 8.3

CentOS 8.3 changed the name of the PowerTools repository to powertools:
https://wiki.centos.org/Manuals/ReleaseNotes/CentOS8.2011#Yum_repo_file_and_repoid_changes

With this repository disabled, DevStack fails to install libyaml-devel,
which causes a failure to install many packages. In my environment
DevStack stopped with an error caused by a missing wget.

Keep the command using the old repository name, for compatibility with
older CentOS releases.

Change-Id: I5541a8aee8467abf10ce8a10d770618bdd693f02
1 file changed