Support multidex run-test with Jack

Updates default-build script to compile multidex run-tests with
Jack. Such test needs a 'multidex.jpp' file specifying how to
partition classes in the output dex files (mainly how to stick some
classes in the classes.dex file and others in a classes2.dex file).

Bug: 19467889
Change-Id: I2500967ba951218c5b03166b3586a576d6dc8749