Added fix for RPC port detection

[dat-boris]

Fixes: #5713
Related: #5590
Merge before/after: None

Description

In #5713 we discover that the new port detection logic does not apply
to GRPC startup, which default starts on Mac on IPv4 loopback.

Test plan:

Locally run multiple version of skaffold, ensure that none
of them have issues with starting up their own RPC server.

Instead of crashing, it now correctly skip previous ports used by RPC

WARN[0000] starting gRPC server on port 50053. (50051 is already in use) 
WARN[0000] starting gRPC HTTP server on port 50054. (50052 is already in use) 

[dat-boris]

This is my first PR for skaffold so any review comments are much appreciated. I know also #5590 so would be nice if we can confirm that on Windows machine this will not cause any regression (hopefully shouldn't do - it was a revert to previous behaviour for GRPC).

[codecov]

Codecov Report

Merging #5715 (db6c8c2) into master (7d1db11) will decrease coverage by 0.02%.
The diff coverage is 70.58%.

@@            Coverage Diff             @@
##           master    #5715      +/-   ##
==========================================
- Coverage   70.87%   70.85%   -0.03%     
==========================================
  Files         421      421              
  Lines       16050    16055       +5     
==========================================
  Hits        11375    11375              
- Misses       3844     3846       +2     
- Partials      831      834       +3     

Impacted Files	Coverage Δ
...kubernetes/portforward/port_forward_integration.go	0.00% <0.00%> (ø)
pkg/skaffold/util/port.go	89.28% <72.72%> (-2.88%)	⬇️
...affold/kubernetes/portforward/kubectl_forwarder.go	69.71% <100.00%> (ø)
...g/skaffold/kubernetes/portforward/pod_forwarder.go	82.00% <100.00%> (ø)
...ffold/kubernetes/portforward/resource_forwarder.go	87.71% <100.00%> (ø)
pkg/skaffold/server/server.go	41.96% <100.00%> (ø)
pkg/skaffold/docker/image.go	78.34% <0.00%> (-1.39%)	⬇️

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[MarlonGamez]

Thanks for opening this @dat-boris ! Have a few tiny nit comments :)

[briandealwis]

Sorry @dat-boris for the delay — I held off as I wanted to check how we were using GetAvailablePort(). Prior to #5670 we were explicitly passing the interface. I think we should restore that aspect and I'll push that change here.

[MarlonGamez]

lgtm, thanks @dat-boris for the contribution :)

[dat-boris]

Thank you @briandealwis @MarlonGamez for the reviews! Yeah it make sense to revert to the old GetAvailablePort and improve the check!