Support tunneling to masters over SSH for e2e tests

[smarterclayton]

Workers are now private, which means we can't directly connect to
them. For now, make the e2e tests tolerate a bastion hop by
proxying the SSH connection from a given instance.

TODO:

• needs to go upstream in some form Support e2e testing via a bastion host for SSH commands kubernetes/kubernetes#72286
• need to revert pkg/asset/machines/aws/machinesets: Give workers public IPs (for now) installer#927 because we can't access the external IP anyway in Revert "pkg/asset/machines/aws/machinesets: Give workers public IPs (for now)" installer#970
• should probably autodetect the bastion if we can, or just change release to set it
  Set KUBE_SSH_BASTION and KUBE_SSH_KEY_PATH in installer tests release#2469

Blocks moving away from e2e-gcp because some tests still depend on SSH https://openshift-gce-devel.appspot.com/build/origin-ci-test/logs/release-openshift-origin-installer-e2e-aws-all-4.0/18/

[smarterclayton]

/retest

[smarterclayton]

/test e2e-gcp

[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/test e2e-aws-all

[openshift-ci-robot]

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[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/test e2e-aws-all

[smarterclayton]

/skip e2e-aws-all

[smarterclayton]

/retest

[openshift-ci-robot]

@smarterclayton: The following tests failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
ci/prow/e2e-gcp	c6655ab	link	/test e2e-gcp
ci/prow/e2e-aws-all	c6655ab	link	/test e2e-aws-all

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[smarterclayton]

Node port tests still need to be fixed, that will be a follow up.

@soltysh I will create a pick of this to your rebase branch, but with this change there should only be 10 or so aws-all failures (taints and node ports are the only two broken areas)