oeqa/runtime/login: Proof of concept for screenshot testcases

oeqa/runtime/login: Proof of concept for screenshot testcases

This takes the work rburton did on image screenshot testing and
expands it.

Right now this works with most of the qemu based machines except for

- qemuppc64
- qemuarmv5
- qemuriscv32
- qemuloongarch64

See "Known Issues" further down.

This test takes a screendump of a qemu image, blanks out the clock
and compares it to an image we have on record. If the diff is exact,
the test passes. If not, it stores the image in build/failed-images and
fails out.

In order to enable this test, you will need meta-openembedded/meta-oe in
your bblayers.conf for imagemagick and the following in local.conf:

IMAGE_CLASSES += "testimage"
TEST_SUITES = "login"
TESTIMAGEDEPENDS:append:qemuall = " imagemagick-native:do_populate_sysroot "

Known Issues
------------

The main issue is that I've yet to find a gating factor that would allow
me to tell when the qemu instance is fully up and rendered. I've tried a
few tactics here, (dbus-wait, qmp) but for now a disgusting
time.sleep(30) is there.

You can replicate this by running qemumips. The screen load takes forever,
but you even see it on qemux86 where the Home and Workspace Switch icons
will sometimes take a while to fully load.

Eventually I'm going to have to take multiple screenshots and compare
them, but then you get into the issue where the question is, is the diff
greater than 0 because it hasn't fully loaded or something is actually
incorrect.

There are the issues I know about:

   - runqemu qemuppc64 comes up blank.
   - qemuarmv5 comes up with multiple heads but sending "head" to screendump.
     seems to create a png with a bad header.
   - qemuriscv32 and qemuloongarch64 don't work with testimage apparently?
   - qemumips64 is missing mouse icon.
   - qemumips takes forever to render and is missing mouse icon.
   - qemuarm and qemuppc return incorrect width
   - All images have home and screen flipper icons not always rendered fully at first.
     The sleep seems to help this out some, depending on machine load.

Signed-off-by: Eilís 'pidge' Ní Fhlannagáin <pidge@baylibre.com>
Co-authored-by: Ross Burton <ross.burton@arm.com>
Co-authored-by: Eilís 'pidge' Ní Fhlannagáin <pidge@baylibre.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>