Use faster build for the default minikube target

[afbjorklund]

When we are doing the "cross" compile targets, we
force rebuilding all packages (up-to-date or not).

For the default native target "out/minikube", we
can do a much faster build (10x!), for development.

Leaving all the cross target to rebuild, as before.

Also the _test.go files are only used for unit tests.

---

On my machine it takes about 50 seconds, to rebuild all the 645 packages...

real	0m47.801s
user	2m36.732s
sys	0m8.620s

Doing an incremental build takes only 6 seconds, and is much more usable.

real	0m6.077s
user	0m7.368s
sys	0m0.928s

Interesting flags to go build:

The build flags are shared by the build, clean, get, install, list, run,
and test commands:

	-a
		force rebuilding of packages that are already up-to-date.
	-n
		print the commands but do not run them.
	-v
		print the names of packages as they are compiled.
	-x
		print the commands.

I used -v to get the 645 lines.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: afbjorklund

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [afbjorklund]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-io]

Codecov Report

Merging #5749 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #5749   +/-   ##
=======================================
  Coverage   36.58%   36.58%           
=======================================
  Files         110      110           
  Lines        8096     8096           
=======================================
  Hits         2962     2962           
  Misses       4745     4745           
  Partials      389      389

[tstromberg]

@minikube-bot OK to test

[tstromberg]

That's a really impressive improvement. I look forward to merging this :)

[medyagh]

the mac os test failures I seen on other PRs, not related to this PR

[afbjorklund]

Need to add at least go.mod to the list of dependencies, when not rebuilding everything.

[afbjorklund]

Also had broken the default build in Docker, i.e. BUILD_IN_DOCKER=y make

[minikube-bot]

Old binary: [177.933725752 182.630983241 192.264802579]
New binary: [176.728872042 193.192061635 173.00130522]
Average Old: 184.276504
Average New: 180.974080

[medyagh]

afbjorklund please merge this when you feel ready !