python3-evdev should be a Depends for autopilot-touch

I ran into a weird dependency issue while working on https://code.launchpad.net/~canonical-platform-qa/webbrowser-app/autopkgtest/+merge/256858 to create dep8 tests that can run on both qemu and the phone, I had to make python3-evdev an explicit dep of the test.

When I don't (revno 978) but use needs-recommends instead, some test fail with:

14:29:57.292 INFO __init__:286 - You cannot create a Mouse on the devices where X11 is not available. consider using a Touch or Pointer device. For more information, see: http://unity.ubuntu.com/autopilot/api/input.html#autopilot-unified-input-system
14:29:57.730 ERROR testresult:44 - ERROR: webbrowser_app.tests.test_tabs.TestTabsView.test_close_current_tab
14:29:57.732 ERROR testresult:44 - traceback-1: {{{
Traceback (most recent call last):
  File "/tmp/adt-run.wIoiKP/deps/usr/lib/python3/dist-packages/autopilot/utilities.py", line 348, in action_on_test_end
    obj.on_test_end(test_instance)
  File "/tmp/adt-run.wIoiKP/deps/usr/lib/python3/dist-packages/autopilot/input/_X11.py", line 496, in on_test_end
    move_mouse_to_screen(0)
  File "/tmp/adt-run.wIoiKP/deps/usr/lib/python3/dist-packages/autopilot/display/__init__.py", line 71, in move_mouse_to_screen
    Mouse.create().move(x, y, False)
  File "/tmp/adt-run.wIoiKP/deps/usr/lib/python3/dist-packages/autopilot/input/__init__.py", line 293, in create
    "Cannot create a Mouse on devices where X11 is not available."
RuntimeError: Cannot create a Mouse on devices where X11 is not available.

My gut feeling is that some recommends are installed on the phone and they shouldn't (may be python3-xlib) because that confuse autopilot about which platform it's running on (or something ;)

Discussing the issue on IRC:

<vila> pitti: about needs-recommends, I wondered if python3-evdev should move to Depends in autopilot-touch ?
<pitti> vila: for -touch, I think yes