Support CentOS Stream 9

This patch includes changes required to run devstack on CentOS Stream 9
which has been already published in official repos by CentOS team [1]:

- Add RDO deps repository for CS9.
- remove xinetd package from installation for swift. Note that
  rsync-daemon is installed which should work fine.
- Replace genisoimage by xorriso in CS9.
- Use /etc/os-release to identify the distro in CS9 as it doesn't
  provide lsb_release command.
- Use pip from rpm package instead of from get-pip.py as done in Fedora.
- Add non-voting job devstack-platform-centos-9-stream to the check
  pipeline.

Change-Id: Ic67cddabd5069211dc0611994b8b8360bcd61bef
diff --git a/lib/nova b/lib/nova
index 9aae2c4..31b7642 100644
--- a/lib/nova
+++ b/lib/nova
@@ -479,7 +479,8 @@
     fi
 
     # nova defaults to genisoimage but only mkisofs is available for 15.0+
-    if is_suse; then
+    # rhel provides mkisofs symlink to genisoimage or xorriso appropiately
+    if is_suse || is_fedora; then
         iniset $NOVA_CONF DEFAULT mkisofs_cmd /usr/bin/mkisofs
     fi