bugfix: CDN == "source" does not request pieces from source

[m0nstermind]

by dfget having suprnodes was configured with explicily defined port

Ⅰ. Describe what this PR did

When supernode listens on non default port ( e.g. other than 80 for http ) the CDN Pattern: source ( to request pieces from source url ) does not work. dfget try to load pieces for the first time from supernode and fail, because supernode does not have them.

The source of this is in comparation performed by dfget at power_client.go, which compares piece destination ip, received by downloader to the url of supernode PowerClient is initialized with ( which comes in form ip:port ). In case of default port value, it is omitted from configration and this check passes and always fails for non default port values.
The PR fixes this to compare ip to ip.

Ⅱ. Does this pull request fix one issue?

none

Ⅲ. Why don't you add test cases (unit test/integration test)?

The fix is trivial

Ⅳ. Describe how to verify it

Prepare supernode.yaml with

base:
  cdnPattern: source
  listenPort: 5002

run supernode without running nginx

run dfget with
dfget --node 127.0.0.1:5002 http://source/url/to/get

dfget will fail to download any pieces from source url, trying to get it from 127.0.0.1:8001 ( the default download port of supernode )

Ⅴ. Special notes for reviews

none

[pouchrobot]

We found this is your first time to contribute to Dragonfly, @m0nstermind
👏 We really appreciate it.
Just remind that you have read the contribution guide: https://github.com/dragonflyoss/Dragonfly/blob/master/CONTRIBUTING.md
If you didn't, you should do that first. If done, welcome again and please enjoy hacking! 🍻

[jim3ma]

Please sign your commit with git commit -s --amend, then force push it.
Thanks

[m0nstermind]

BTW unit test failed with
image_preheater_test.go:38: Get https://registry.cn-zhangjiakou.aliyuncs.com/v2/acs/alpine/manifests/3.6: net/http: TLS handshake timeout

which, i believe is not about this PR, but due to connectivity problems with registry.cn-zhangjiakou.aliyuncs.com

[starnop]

LGTM.
also cc/ @jim3ma

[starnop]

BTW unit test failed with
image_preheater_test.go:38: Get https://registry.cn-zhangjiakou.aliyuncs.com/v2/acs/alpine/manifests/3.6: net/http: TLS handshake timeout

which, i believe is not about this PR, but due to connectivity problems with registry.cn-zhangjiakou.aliyuncs.com

I have rerun the CI.

[codecov-io]

Codecov Report

Merging #1501 (9c4b244) into master (0639b49) will decrease coverage by 1.45%.
The diff coverage is 46.66%.

@@            Coverage Diff             @@
##           master    #1501      +/-   ##
==========================================
- Coverage   50.76%   49.31%   -1.46%     
==========================================
  Files         145      145              
  Lines        9557     8381    -1176     
==========================================
- Hits         4852     4133     -719     
+ Misses       4309     3861     -448     
+ Partials      396      387       -9     

Impacted Files	Coverage Δ
...et/core/downloader/p2p_downloader/client_writer.go	8.47% <0.00%> (-0.06%)	⬇️
...t/core/downloader/p2p_downloader/p2p_downloader.go	1.85% <0.00%> (-0.24%)	⬇️
supernode/daemon/mgr/preheat/file_preaheater.go	2.43% <ø> (-3.69%)	⬇️
supernode/daemon/mgr/preheat/preheat_service.go	0.00% <0.00%> (ø)
supernode/daemon/mgr/cdn/manager.go	22.55% <75.00%> (+1.69%)	⬆️
...get/core/downloader/p2p_downloader/power_client.go	53.12% <100.00%> (+0.29%)	⬆️
supernode/daemon/mgr/task/manager.go	29.26% <100.00%> (+0.69%)	⬆️
supernode/server/metrics.go	70.31% <100.00%> (+0.16%)	⬆️
supernode/store/store.go	44.44% <0.00%> (-9.73%)	⬇️
supernode/daemon/mgr/cdn/cdn_util.go	37.50% <0.00%> (-8.66%)	⬇️
... and 143 more

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