Don't exit on 'k6 cloud -q' just don't print progress

[mstoykov]

fixes #1371

[codecov-io]

Codecov Report

Merging #1702 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1702      +/-   ##
==========================================
- Coverage   72.34%   72.34%   -0.01%     
==========================================
  Files         176      176              
  Lines       13535    13533       -2     
==========================================
- Hits         9792     9790       -2     
  Misses       3130     3130              
  Partials      613      613              

Flag	Coverage Δ
#ubuntu	72.33% <ø> (+0.02%)	⬆️
#windows	70.87% <ø> (-0.02%)	⬇️

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Impacted Files	Coverage Δ
cmd/cloud.go	6.85% <ø> (+0.07%)	⬆️
core/engine.go	90.95% <0.00%> (-2.02%)	⬇️
lib/testutils/minirunner/minirunner.go	86.04% <0.00%> (+4.65%)	⬆️

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