getDisplayDecorationSupport test: allow errors

Allow getDisplayDecorationSupport to return an error, and treat that as
unsupported. This allows Cuttlefish, which, with
I91105fc3345dbd75aeb0b102f3f0138fa33120c0, returns Unsupported, to pass
the test.

Bug: 209458568
Test: this
Change-Id: I8e17d3c0ca0ac4eacb0b5e4c8ae540f271e68a23