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/tools/install_pip.sh b/tools/install_pip.sh
index c72dc89..259375a 100755
--- a/tools/install_pip.sh
+++ b/tools/install_pip.sh
@@ -118,7 +118,7 @@
     configure_pypi_alternative_url
 fi
 
-if is_fedora && [[ ${DISTRO} == f* ]]; then
+if is_fedora && [[ ${DISTRO} == f* || ${DISTRO} == rhel9 ]]; then
     # get-pip.py will not install over the python3-pip package in
     # Fedora 34 any more.
     #  https://bugzilla.redhat.com/show_bug.cgi?id=1988935