utils: fix excessive refresh frequency when BR_LOG_TO_TERM=1 (#334)

[sre-bot]

cherry-pick #334 to release-4.0

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What problem does this PR solve?

Fix item 5 of #259.

What is changed and how it works?

1. Do not start the progress bar before it was fully configured (so that the refresh rate can really be respected).
2. Further increased the refresh rate when BR_LOG_TO_TERM=1 from 10s to 2m.
3. Included more progress information into the log when BR_LOG_TO_TERM=1:

[2020/06/04 20:01:14.965 +00:00] [INFO] [progress.go:113] [progress] [step="Full restore"] [progress=29.18%] [count="700 / 2399"] [speed="11 p/s"] [elapsed=48s] [remaining=2m34s]

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)
  • Execute BR manually with BR_LOG_TO_TERM=1 and inspect the output.

Code changes

Side effects

Related changes

Release Note

• Reduced the excessive refresh rate of progress logs when logging to terminal (e.g. when using K8s).

[codecov]

Codecov Report

Merging #341 into release-4.0 will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           release-4.0     #341   +/-   ##
============================================
  Coverage        73.30%   73.30%           
============================================
  Files               51       51           
  Lines             5645     5645           
============================================
  Hits              4138     4138           
  Misses            1010     1010           
  Partials           497      497           

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