Add test for signal handling

[dgageot]

Signed-off-by: David Gageot [email protected]

[codecov-io]

Codecov Report

Merging #917 into master will increase coverage by 0.36%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #917      +/-   ##
==========================================
+ Coverage   39.01%   39.38%   +0.36%     
==========================================
  Files          60       61       +1     
  Lines        2609     2613       +4     
==========================================
+ Hits         1018     1029      +11     
+ Misses       1478     1471       -7     
  Partials      113      113

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/dev.go	0% <ø> (ø)	⬆️
cmd/skaffold/app/cmd/signals.go	100% <100%> (ø)

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[balopat]

LGTM