ImageWriter: Attach non-opaque Images as well.

With all the work under the hood of ImageReader/Writer in the last few
releases, this is much more straightforward to enable.

Only trick is to ensure that the Image detached from the ImageReader
correctly clears out its planes, if present.

Bug: 19962027
Test: Camera CTS still passes on angler, sailfish, ryu
Change-Id: Ic8a1f3e2f45cf15971d76e308a5af25eb2fd66f1