Pin apache-harmony-tests{,-hostdex} to java_version 1.8

This decouples the class file version fed to jarjar from the
current default class file version.
Bug: 72703434
Test: EXPERIMENTAL_USE_OPENJDK9=true USE_R8=true make checkbuild docs
      (in a client where CL http://r.android.com/596874 was reverted)

Change-Id: I1436f9eb7713b1d55714950888492db5dfdd10aa
1 file changed