Migrate builder tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2 to LUCI.

Buildbot: https://ci.chromium.org/buildbot/tryserver.chromium.linux/linux_layout_tests_slimming_paint_v2
LUCI: https://ci.chromium.org/buildbucket/luci.chromium.try/LUCI%20linux_layout_tests_slimming_paint_v2

I will be posting updates on changes of the migration status.
For the latest status, see
https://luci-migration-dev.appspot.com/masters/tryserver.chromium.linux/builders/linux_layout_tests_slimming_paint_v2