This expands get, getmtime, exportKey, getKeyCharacteristcs and begin to accept a uid to run as. This is only for system to use keys owned by Wifi and VPN, and not something that can be used to do operations as another arbitrary application. Cherry-picked from 5bbf04803f050296a6deab10a3c7104743c4e38c Bug: 23978113 Change-Id: I06aa089859edc934a5415e3b184b917d6d171ae2