This fix tries to address the issue raised in #21976 and allows the options of `--dns`, `--dns-search`, `--dns-opt` and `--net=host` to work at the same time. The documentation has been updated and additional tests have been added to cover this change. This fix fixes #21976. Signed-off-by: Yong Tang <yong.tang.github@outlook.com> Upstream-commit: 23821fe5867427fa36c265bc994b1a2c3cf9b21f Component: engine