spread: allow setting SPREAD_DEBUG_EACH=0 to disable debug-each section

[zyga]

This aids in interactive debugging where we don't want to scroll through
mountains of unrelated syslog messages and we are running interactively
so we can inspect anything we want. The default stays the same as before
so spread runs on linode will show debug on failure.

Signed-off-by: Zygmunt Krynicki zygmunt.krynicki@canonical.com

[codecov-io]

Codecov Report

Merging #4027 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4027      +/-   ##
==========================================
- Coverage   75.88%   75.88%   -0.01%     
==========================================
  Files         431      431              
  Lines       36915    36915              
==========================================
- Hits        28014    28012       -2     
- Misses       6948     6950       +2     
  Partials     1953     1953

Impacted Files	Coverage Δ
overlord/ifacestate/helpers.go	62.33% <0%> (-0.67%)	⬇️

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