Add apache-xml to boot class path for tests.

And partially revert
    7a85e70b
and fully revert
    d4291d68
to re-enable tests.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: m test-art-target-gtest
Test: testrunner.py --target --optimizing
Test: run-libcore-tests --mode=host --variant=X64
Test: run-jdwp-tests --mode=host --variant=X64
Test: run-libcore-tests --mode=target --variant=X64
Test: run-jdwp-tests --mode=target --variant=X64
Bug: 120526172
Change-Id: I5af4853cae84bfc4807d98668b2da2fd9c5fc22e