Remove dependency on nc for port checking

[jiridanek]

fixes #481

[jiridanek]

I've already signed the CLA at https://cla-assistant.io/twitter/scoot; not sure why the CLA check is not updating.

[codecov-io]

Codecov Report

Merging #484 (55b9c76) into master (f267b05) will decrease coverage by 1.50%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #484      +/-   ##
==========================================
- Coverage   53.24%   51.73%   -1.51%     
==========================================
  Files         116      123       +7     
  Lines        8127     8385     +258     
==========================================
+ Hits         4327     4338      +11     
- Misses       3291     3538     +247     
  Partials      509      509              

Impacted Files	Coverage Δ
scheduler/setup/ports.go	100.00% <100.00%> (ø)
scheduler/setup/builder.go	0.00% <0.00%> (ø)
scheduler/setup/workers.go	0.00% <0.00%> (ø)
scheduler/setup/cmds.go	0.00% <0.00%> (ø)
scheduler/setup/api.go	0.00% <0.00%> (ø)
scheduler/setup/sched.go	0.00% <0.00%> (ø)
scheduler/setup/setup.go	0.00% <0.00%> (ø)

---

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[codecov-commenter]

Codecov Report

Merging #484 (28612da) into master (d37b89c) will decrease coverage by 1.43%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #484      +/-   ##
==========================================
- Coverage   52.59%   51.15%   -1.44%     
==========================================
  Files         113      120       +7     
  Lines        8381     8638     +257     
==========================================
+ Hits         4408     4419      +11     
- Misses       3464     3710     +246     
  Partials      509      509              

Impacted Files	Coverage Δ
scheduler/setup/ports.go	100.00% <100.00%> (ø)
scheduler/setup/cmds.go	0.00% <0.00%> (ø)
scheduler/setup/builder.go	0.00% <0.00%> (ø)
scheduler/setup/setup.go	0.00% <0.00%> (ø)
scheduler/setup/workers.go	0.00% <0.00%> (ø)
scheduler/setup/sched.go	0.00% <0.00%> (ø)
scheduler/setup/api.go	0.00% <0.00%> (ø)

---

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Δ = absolute <relative> (impact), ø = not affected, ? = missing data
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