.oniro-ci: enable wic image debug mode for LAVA testing

LAVA needs a writable directory to deploy test cases, and many test
cases only work with root user.

The debug mode can be disabled by overwriting the
CI_ONIRO_BB_LOCAL_CONF_plus_equals_INHERIT variable at build job level.

Signed-off-by: Chase Qi <chase.qi@linaro.org>