Support querying systemd container information

systemd writes a /run/systemd/container file in any container it starts
to make it really easy to detect the container type. This adds support
for detecting systemd-nspawn containers (and any other container format
that will write data there for compatibility).

lib/ansible/module_utils/facts.py

@@ -2394,6 +2394,12 @@ class LinuxVirtual(Virtual):
                 self.facts['virtualization_role'] = 'guest'
             return
 
+        systemd_container = get_file_content('/run/systemd/container')
+        if systemd_container:
+            self.facts['virtualization_type'] = systemd_container
+            self.facts['virtualization_role'] = 'guest'
+            return
+
         if os.path.exists('/proc/1/cgroup'):
             for line in get_file_lines('/proc/1/cgroup'):
                 if re.search(r'/docker(/|-[0-9a-f]+\.scope)', line):