test: rework the output for the xkeyboard-config layout tester

test: rework the output for the xkeyboard-config layout tester

The previous output is largely unusable. The result in the CI test runs is a 6GB
file with every compiled keymap in it and while we can grep for ERROR, it's not
particularly useful.

Let's change this and print out YAML instead - that can be machine-processed.
This patch adds a new parent class that prints itself in YAML format,
the tool invocations are child classes of that class. The result looks like this:

Example output:
- rmlvo: ["evdev", "pc105", "us", "haw", "grp:rwin_switch"]
  cmd: "xkbcli-compile-keymap --verbose --rules evdev --model pc105 --layout us --variant haw --options grp:rwin_switch"
  status: 0
- rmlvo: ["evdev", "pc105", "us", "foo", ""]
  cmd: "xkbcli-compile-keymap --verbose --rules evdev --model pc105 --layout us --variant foo"
  status: 1
  error: "failed to compile keymap"

Special status codes are: 99 for "unrecognized keysym" and 90 for "Cannot open
display" in the setxkbmap case.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>