tests: Introduce hotplug hot-unplug unit test

This test checks the code-paths for camera's hotplugged and
unplugged support. It is based on bind/unbind of a UVC device
from sysfs. Hence, this test requires root permissions to run
and should have at least one already bound UVC device present
in the system.

Signed-off-by: Umang Jain <email@uajain.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

test/meson.build

@@ -30,6 +30,7 @@ internal_tests = [
     ['event-thread',                    'event-thread.cpp'],
     ['file',                            'file.cpp'],
     ['file-descriptor',                 'file-descriptor.cpp'],
+    ['hotplug-cameras',                 'hotplug-cameras.cpp'],
     ['message',                         'message.cpp'],
     ['object',                          'object.cpp'],
     ['object-invoke',                   'object-invoke.cpp'],