tests/dbus-runner: Move logind helper into a separate file

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2618>

src/tests/logind_helpers.py

@@ -0,0 +1,21 @@
+import dbus
+import os
+import re
+
+def open_file_direct(major, minor):
+    sysfs_uevent_path = '/sys/dev/char/{}:{}/uevent'.format(major, minor)
+    sysfs_uevent = open(sysfs_uevent_path, 'r')
+    devname = None
+    for line in sysfs_uevent.readlines():
+        match = re.match('DEVNAME=(.*)', line)
+        if match:
+            devname = match[1]
+            break
+    sysfs_uevent.close()
+    if not devname:
+        raise dbus.exceptions.DBusException(f'Device file {major}:{minor} doesn\\\'t exist',
+                                            major=major, minor=minor)
+    fd = os.open('/dev/' + devname, os.O_RDWR | os.O_CLOEXEC)
+    unix_fd = dbus.types.UnixFd(fd)
+    os.close(fd)
+    return (unix_fd, False)