ENH: make --follow "faster"

[yarikoptic]

See individual commits.

The last one -- I feel this might be of interest to other places as well were dynamic sleeping/reporting is desired, so might be generalized at some point.

[codecov[bot]]

Codecov Report

Merging #519 into master will increase coverage by 0.10%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #519      +/-   ##
==========================================
+ Coverage   89.47%   89.58%   +0.10%     
==========================================
  Files         148      148              
  Lines       12290    12299       +9     
==========================================
+ Hits        10997    11018      +21     
+ Misses       1293     1281      -12     

Impacted Files	Coverage Δ
reproman/support/jobs/submitters.py	79.25% <100.00%> (+1.04%)	:arrow_up:
reproman/interface/tests/test_run.py	98.46% <0.00%> (-1.16%)	:arrow_down:
reproman/interface/jobs.py	98.00% <0.00%> (-1.00%)	:arrow_down:
...eproman/interface/tests/test_backend_parameters.py	100.00% <0.00%> (+4.34%)	:arrow_up:
reproman/tests/skip.py	97.75% <0.00%> (+4.49%)	:arrow_up:
reproman/distributions/tests/test_venv.py	98.07% <0.00%> (+10.57%)	:arrow_up:

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[yarikoptic]

Re first sleep removal - I guess time will show indeed.