Make completion work again

[briandealwis]

Fixes: #5960

This PR prevents redirecting output for the internal spf13/cobra commands used for handling completion support. Use cmd.Name() as cmd.Use has [command-line] appended to the name for these internal commands.

[gsquared94]

nice, lgtm!

[codecov]

Codecov Report

Merging #6138 (005a6a5) into master (823896b) will increase coverage by 0.00%.
The diff coverage is 35.71%.

@@           Coverage Diff           @@
##           master    #6138   +/-   ##
=======================================
  Coverage   69.94%   69.95%           
=======================================
  Files         478      478           
  Lines       18286    18287    +1     
=======================================
+ Hits        12791    12793    +2     
  Misses       4548     4548           
+ Partials      947      946    -1     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/cmd.go	68.75% <35.71%> (+0.17%)	⬆️
pkg/skaffold/util/tar.go	50.66% <0.00%> (-5.34%)	⬇️
pkg/skaffold/docker/parse.go	87.14% <0.00%> (+0.95%)	⬆️
pkg/skaffold/docker/image.go	79.53% <0.00%> (+1.39%)	⬆️

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