Rename should behave like create: avoid conflict.

When we create a file that already exists, we try attaching a suffix
like "(1)" to the filename to avoid the conflict.  The newly added
rename method should do the same, since developers may not have
access to delete the conflicting file.

Test: boots, rename via UI, new unit tests
Bug: 31545404
Change-Id: Ie397eebb0fbf98cf079eee3bbbb6c6b7ca627d91