autoconf: add support for openEuler

Add config support for openEuler, so that it set the right sysconfig
dir for openEuler.

And DEFAULT_INIT_SCRIPT is no longer needed since commit "2a34db1bd
Base init scripts for SYSV systems".

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Xinliang Liu <xinliang.liu@linaro.org>
Closes #14241