cluster/executor: implement native SCP download instead of cat

[AstroProfundis]

What problem does this PR solve?

Use native SCP to download file from remote, instead of cat the file content.

What is changed and how it works?

Protocol doc: https://web.archive.org/web/20170215184048/https://blogs.oracle.com/janp/entry/how_the_scp_protocol_works
The implementation is partially inspired by https://github.com/dtylman/scp

Check List

Tests

• Integration test
• Manual test (add detailed scripts or steps below)

Code changes

• Has exported function/method change

Release notes:

cluster: adjust file transferring with remote server to use native SCP

[codecov-commenter]

Codecov Report

Merging #1382 (bb5d8ff) into master (fdadd94) will increase coverage by 28.79%.
The diff coverage is 36.97%.

@@             Coverage Diff             @@
##           master    #1382       +/-   ##
===========================================
+ Coverage   25.34%   54.14%   +28.79%     
===========================================
  Files         265      291       +26     
  Lines       20517    22466     +1949     
===========================================
+ Hits         5201    12165     +6964     
+ Misses      14517     8370     -6147     
- Partials      799     1931     +1132     

Flag	Coverage Δ
cluster	41.83% <35.96%> (?)
dm	24.55% <5.93%> (?)
integrate	48.70% <36.13%> (+33.10%)	⬆️
playground	13.74% <0.00%> (?)
tiup	15.50% <0.00%> (-0.10%)	⬇️
unittest	21.57% <3.38%> (-0.07%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
components/dm/spec/logic.go	78.65% <0.00%> (+78.04%)	⬆️
pkg/cluster/ansible/config.go	0.00% <0.00%> (ø)
pkg/cluster/ctxt/context.go	89.09% <ø> (+89.09%)	⬆️
pkg/cluster/executor/local.go	55.71% <ø> (ø)
pkg/cluster/operation/telemetry.go	0.00% <0.00%> (ø)
pkg/cluster/spec/alertmanager.go	66.12% <0.00%> (+58.06%)	⬆️
pkg/cluster/spec/cdc.go	75.75% <0.00%> (+72.72%)	⬆️
pkg/cluster/spec/drainer.go	58.76% <0.00%> (+56.70%)	⬆️
pkg/cluster/spec/pd.go	68.26% <0.00%> (+53.29%)	⬆️
pkg/cluster/spec/pump.go	69.14% <0.00%> (+48.93%)	⬆️
... and 239 more

---

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[lucklove]

This is not needed.

[lucklove]

/lgtm

[ti-chi-bot]

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• lucklove

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[lucklove]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: bb5d8ff