test: Fix panic on tests that don't schedule to nodes

[jonathan-innis]

Fixes #

Description

Fix a panic on testing that failed to schedule pods to a Machine/Node combination. We should return back a nil Machine if we fail to schedule and pass that back up so that we don't do any binding of that pod to the Machine/Node.

How was this change tested?

make presubmit

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[coveralls]

Pull Request Test Coverage Report for Build 4866606697

• 5 of 8 (62.5%) changed or added relevant lines in 1 file are covered.
• 7 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.09%) to 81.905%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pkg/test/expectations/expectations.go	5	8	62.5%

Files with Coverage Reduction	New Missed Lines	%
pkg/controllers/node/controller.go	7	70.59%

Totals
Change from base Build 4866344853:	0.09%
Covered Lines:	6826
Relevant Lines:	8334

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💛 - Coveralls