test: make TEST-08-INITRD slightly less annoying to debug

Forward journal to console, since we won't have any journal from initrd
and shutdown/exit initrd phases. Also, mention
systemd.journald.max_level_console=debug that is very handy for
debugging initrd shenanigans, but don't use it by default since it
sends a _lot_ of stuff to the serial console, which slows down the test
a lot.

test/TEST-08-INITRD/test.sh

@@ -3,6 +3,10 @@
 set -e
 
 TEST_DESCRIPTION="Test various scenarios involving transition from/to initrd"
+# Note: for debugging systemd.journald.max_level_console=debug might come in handy
+#       as well, but it's not used here since it's _very_ noisy and slows the test
+#       down a lot
+KERNEL_APPEND="${KERNEL_APPEND:-} systemd.journald.forward_to_console=1"
 TEST_NO_NSPAWN=1
 
 # shellcheck source=test/test-functions