Revert "init: disable oneshot_on test"

This reverts commit d30c5115.

This test wasn't flaky, it was failing when not run as root, but that
has been fixed.

Bug: 152630580
Bug: 152637928
Test: this test is okay now
Change-Id: I3b20be2839dae90ffc6a8eeea68f36e532060af1