feature: cli support add --add-host

[lang710]

Signed-off-by: Lang Chi 21860405@zju.edu.cn

Ⅰ. Describe what this PR did

feature: cli support --add-host
--add-host flag can be used to add additional lines to /etc/hosts.

This is a client flag for network setting, --add-host option can be used in host network mode. This option update /etc/hosts inside the container. No change are made to /etc/hosts on the host.

Ⅱ. Does this pull request fix one issue?

NONE.

Ⅲ. Why don't you add test cases (unit test/integration test)? (你真的觉得不需要加测试吗？)

Added.

Ⅳ. Describe how to verify it

root@compatibility:~# pouch run -it  busybox cat /etc/hosts
127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
ff00::0	ip6-mcastprefix
ff02::1	ip6-allnodes
ff02::2	ip6-allrouters
192.168.5.2	bee635290c2f


root@compatibility:~# pouch run -it --add-host=extra:1.2.3.4  busybox cat /etc/hosts
127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
ff00::0	ip6-mcastprefix
ff02::1	ip6-allnodes
ff02::2	ip6-allrouters
1.2.3.4	extra
192.168.5.2	1e4c791dbe8


root@compatibility:~# pouch run -it --add-host=extra:1.2.3.4  --add-host=extra2:2.3.4.5 busybox cat /etc/hosts
127.0.0.1	localhost
::1	localhost ip6-localhost ip6-loopback
fe00::0	ip6-localnet
ff00::0	ip6-mcastprefix
ff02::1	ip6-allnodes
ff02::2	ip6-allrouters
1.2.3.4	extra
2.3.4.5	extra2
192.168.5.2	1e4c791dbe8

Ⅴ. Special notes for reviews

--add-host option can be used in host network mode. Extra network config validation should be provided.

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[ZYecho]

lgtm

[fuweid]

if there is no : in extraHost?

[lang710]

LGTM, here should be some validation before appending the provided extra hosts, I'll fix it later, thx.

[ZYecho]

@fuweid ptal