Keymaster clients need to see all the available devices and figure out
which they want to use. This method finds them all and returns them
in a vector sorted from most secure to least, according to a heuristic
defined in Keymaster::VersionResult::operator<
This CL also makes a few other minor improvements to the support
library, providing more information in VersionResult and adding some
more convenience methods in AuthorizationSetBuilder.
Test: Build & boot
Change-Id: I876238ee9ff72573c30d60e1cec665dd610bcde6
