fix(server): sleep 30m after failed maintenance

[jkowalski]

Fixes #1651
Fixes #1652

[codecov]

Codecov Report

Merging #1684 (db3ea9c) into master (525d161) will decrease coverage by 0.01%.
The diff coverage is 47.05%.

@@            Coverage Diff             @@
##           master    #1684      +/-   ##
==========================================
- Coverage   70.61%   70.60%   -0.02%     
==========================================
  Files         386      387       +1     
  Lines       30775    30786      +11     
==========================================
+ Hits        21733    21735       +2     
- Misses       7362     7371       +9     
  Partials     1680     1680              

Impacted Files	Coverage Δ
internal/clock/now.go	100.00% <ø> (ø)
internal/server/server.go	70.44% <18.18%> (-0.63%)	⬇️
internal/clock/sleep.go	100.00% <100.00%> (ø)
internal/dirutil/mksubdirall.go	92.10% <0.00%> (-7.90%)	⬇️
repo/blob/sftp/sftp_storage.go	55.58% <0.00%> (-2.18%)	⬇️
internal/epoch/epoch_manager.go	89.76% <0.00%> (-0.52%)	⬇️
repo/content/index_v1.go	76.55% <0.00%> (+1.09%)	⬆️
repo/content/content_manager_iterate.go	91.71% <0.00%> (+2.20%)	⬆️
snapshot/snapshotfs/estimate.go	100.00% <0.00%> (+3.33%)	⬆️

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