scylla_raid_setup: workaround for mdmonitor.service issue on CentOS8

On CentOS8, mdmonitor.service does not works correctly when using
mdadm-4.1-15.el8.x86_64 and later versions.
Until we find a solution, let's pinning the package version to older one
which does not cause the issue (4.1-14.el8.x86_64).

Fixes #9540

Closes #9782

dist/common/scripts/scylla_raid_setup

@@ -30,6 +30,8 @@ import distro
 from pathlib import Path
 from scylla_util import *
 from subprocess import run
+import distro
+from pkg_resources import parse_version
 
 if __name__ == '__main__':
     if os.getuid() > 0:
@@ -119,6 +121,25 @@ if __name__ == '__main__':
         pkg_install('xfsprogs')
     if not shutil.which('mdadm'):
         pkg_install('mdadm')
+    # XXX: Workaround for mdmonitor.service issue on CentOS8
+    if is_redhat_variant() and distro.version() == '8':
+        mdadm_rpm = run('rpm -q mdadm', shell=True, check=True, capture_output=True, encoding='utf-8').stdout.strip()
+        match = re.match(r'^mdadm-([0-9]+\.[0-9]+-[a-zA-Z0-9]+)\.', mdadm_rpm)
+        mdadm_version = match.group(1)
+        if parse_version('4.1-14') < parse_version(mdadm_version):
+            repo_data = '''
+[BaseOS_8_3_2011]
+name=CentOS8.3.2011 - Base
+baseurl=http://vault.centos.org/8.3.2011/BaseOS/$basearch/os/
+gpgcheck=1
+enabled=0
+gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial
+'''[1:-1]
+            with open('/etc/yum.repos.d/CentOS-Vault-8.3.repo', 'w') as f:
+                f.write(repo_data)
+            run('dnf downgrade --enablerepo=BaseOS_8_3_2011 -y mdadm', shell=True, check=True)
+            run('dnf install -y python3-dnf-plugin-versionlock', shell=True, check=True)
+            run('dnf versionlock add mdadm', shell=True, check=True)
     try:
         md_service = systemd_unit('mdmonitor.service')
     except SystemdException: