Fix detect of docker as virtualization_type.

Not only match`/docker/`, but also `docker-` followed by a hex-id.

Example (shortened):
```
$ cat /proc/1/cgroup
8:blkio:/system.slice/docker-de73f4d207861cf8757b69213ee67bb234b897a18bea7385964b6ed2d515da94.scope
7:net_cls:/
```

lib/ansible/module_utils/facts.py

@@ -2336,7 +2336,7 @@ class LinuxVirtual(Virtual):
 
         if os.path.exists('/proc/1/cgroup'):
             for line in get_file_lines('/proc/1/cgroup'):
-                if re.search('/docker/', line):
+                if re.search(r'/docker(/|-[0-9a-f]+\.scope)', line):
                     self.facts['virtualization_type'] = 'docker'
                     self.facts['virtualization_role'] = 'guest'
                     return