Store order of the components used by the tests

Previously, the TestContext.Register() method stored all the components
that were available, rather than just the ones that were used by the
tests. That was practically useless for debugging. This change just
stores the ones used by the test.

Bug: 181953909
Test: m nothing
Change-Id: I8589b9b4423133709ab0cfd763bd284a7f47a24a