Hack script improvements

[rifelpet]

Previously we were tracking a list of kops packages in hack/.packages for use by the goimports python scripts. This replaces them with shell scripts (to match all of the other hack scripts) and uses lists of go files rather than packages, removing the need for .packages and all of its dependent python code. The goimports scripts no longer rely on GOPATH.

We'll need to remove the verify-packages prow job before this merges. I will open a test-infra PR to remove verify-packages once the other jobs for this PR pass.

This also updates the apimachinery binaries to be compiled to _output/bin via the hack go submodule to match other development tools. This is the last dependency on GOPATH, because the gengo library that apimachinery uses assumes that the package name that we specify for generated files will be located at $GOPATH/src/$PACKAGE. See the issue mentioned in Makefile for more info.

Lastly this has the pki unit tests ignore KOPS_RSA_PRIVATE_KEY_SIZE. This way we can have the env var set in our terminal to make the integration tests faster while not affecting the pki unit tests.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: rifelpet

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[k8s-ci-robot]

@rifelpet: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
pull-kops-verify-packages	4fc2939	link	/test pull-kops-verify-packages

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[hakman]

/lgtm