server: Enforce a minimum timeout for segment upload

[victorges]

What does this pull request do? Explain your changes. (required)
This is to fix the segment upload timeout for really short segments, which I
found to be an issue when investigating frequent timeouts in VOD tests.

In this case (logs), there is a frequent header timeout happening in the tests,
and even by increasing the retries and adding some backoff logic, it seems to keep
happening pretty often.

I then noticed that it always happened with the same segment of the test video, and
when segmenting it locally with the same code I found that this segment has a duration
of 533ms (and only so short cause it's the last seg in the file).

This means that the upload timeout given to it would be a mere 250ms, which
can easily be hit for longer round-trip times to orchestrators even if they would be able to
respond healthily.

Specific updates (required)

• Make MinSegmentUploadTimeout be a minimum instead of just a default

How did you test each of these updates (required)
Ran automatic tests.

Does this pull request close any open issues?
No.

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[leszko]

Good fix, thanks @victorges 👍

[codecov]

Codecov Report

Merging #2541 (4d8d907) into master (6a212e7) will increase coverage by 0.01511%.
The diff coverage is 100.00000%.

@@                 Coverage Diff                 @@
##              master       #2541         +/-   ##
===================================================
+ Coverage   54.69427%   54.70938%   +0.01510%     
===================================================
  Files             95          95                 
  Lines          19854       19854                 
===================================================
+ Hits           10859       10862          +3     
+ Misses          8390        8387          -3     
  Partials         605         605                 

Impacted Files	Coverage Δ
common/util.go	61.58537% <ø> (ø)
server/segment_rpc.go	78.72969% <100.00000%> (ø)
discovery/db_discovery.go	70.75812% <0.00000%> (+1.08303%)	⬆️

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