Link to magic constants used by AndroidKeyStore API.

This updates the Javadocs of AndroidKeyStore methods which take
constants defined in KeyStoreKeyProperties to contain a link to
the corresponding set of constants and an example of a couple of
accepted constants, to make it easier to understand and find out
what constants to use.

Bug: 18088752
Change-Id: I338134ef136db62a7caca782cb59dbebdc996670