feature: dns configuration for cri manager

[YaoZengzeng]

Signed-off-by: YaoZengzeng [email protected]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

fixes part of #635

Ⅲ. Describe how you did it

First, we create a file /var/lib/pouch/sandbox/${sandbox id}/resolv.conf for every sandbox.

If the pod has configured the DNS configuration, then we write it to the file created above, else we copy the content of /etc/resolv.conf in host to it.

Finally we mount the file to every container's /etc/resolv.conf, then every container in the same pod will have the same DNS configuration :)

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[pouchrobot]

ping @YaoZengzeng

CI fails according integration system.
Please refer to the CI failure Details button to corresponding test, and update your PR to pass CI.

If this is flaky test, welcome to track this with profiling an issue.

build url: https://travis-ci.org/alibaba/pouch/builds/354230101
build duration: 1045s

[codecov-io]

Codecov Report

Merging #912 into master will decrease coverage by 0.1%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #912      +/-   ##
==========================================
- Coverage   13.66%   13.56%   -0.11%     
==========================================
  Files         121      121              
  Lines        7667     7725      +58     
==========================================
  Hits         1048     1048              
- Misses       6529     6587      +58     
  Partials       90       90

Impacted Files	Coverage Δ
daemon/mgr/cri.go	0% <0%> (ø)	⬆️
daemon/mgr/cri_utils.go	30.56% <0%> (-3.56%)	⬇️

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[YaoZengzeng]

@allencloud PTAL.

[allencloud]

LGTM