bugfix: judge enablement of libnetwork resolver by network mode

[mathspanda]

Signed-off-by: mathspanda [email protected]

Ⅰ. Describe what this PR did

The PR is to judge whether enabling embedded dns server by network mode.
If network mode is user-defined, container uses embedded dns server.
If not, container uses resolv.conf file on host directly.

Ⅱ. Does this pull request fix one issue?

Issue #2362

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

None

Ⅳ. Describe how to verify it

# content of resolv.conf file is the same with one on host
pouch run busybox cat /etc/resolv.conf

# content of resolv.conf file contains "nameserver 127.0.0.11"
pouch run --net ns1 busybox cat /etc/resolv.conf

Ⅴ. Special notes for reviews

None

[codecov]

Codecov Report

Merging #2364 into master will increase coverage by 0.23%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2364      +/-   ##
==========================================
+ Coverage   67.85%   68.09%   +0.23%     
==========================================
  Files         265      265              
  Lines       18211    18210       -1     
==========================================
+ Hits        12357    12400      +43     
+ Misses       4421     4393      -28     
+ Partials     1433     1417      -16

Flag	Coverage Δ
#criv1alpha1test	31.67% <77.77%> (+0.11%)	⬆️
#criv1alpha2test	35.48% <77.77%> (-0.09%)	⬇️
#integrationtest	39.48% <100%> (-0.01%)	⬇️
#nodee2etest	33.19% <77.77%> (+0.38%)	⬆️
#unittest	25.31% <0%> (ø)	⬆️

Impacted Files	Coverage Δ
daemon/mgr/network_utils.go	37.2% <100%> (+9.3%)	⬆️
daemon/mgr/container.go	59.17% <100%> (+0.17%)	⬆️
apis/server/utils.go	71.15% <0%> (-3.85%)	⬇️
daemon/mgr/spec_linux.go	74.77% <0%> (-0.61%)	⬇️
cri/v1alpha1/cri.go	61.03% <0%> (+0.32%)	⬆️
ctrd/container.go	59.28% <0%> (+0.47%)	⬆️
daemon/mgr/network.go	69.61% <0%> (+0.47%)	⬆️
cri/v1alpha2/cri_utils.go	90.85% <0%> (+0.57%)	⬆️
daemon/mgr/container_utils.go	84.04% <0%> (+0.61%)	⬆️
... and 9 more

[mathspanda]

@rudyfly PTAL.

[allencloud]

Could you add me as a friend on wechat for further discussion. my account is shlallen. @mathspanda

[rudyfly]

@mathspanda Thank you for your contributions, LGTM