Refactor ChangeInserter's setDraft to match PatchSetInserter's

The `setDraft` method in ChangeInserter can only set the status to
draft; it cannot toggle it.

Change it to be able to toggle the status between draft and new,
making it consistent with the way the method of the same name works
in PatchSetInserter.

Change-Id: Iead2e62701c6b5c90a33efcda35b2e144fd67ccf
2 files changed