Fix remote execution of r8 and d8 in make

1. The location of the r8.jar and d8.jar files was no longer correct.
2. $(JAVA) was not defined before rbe.mk was included.
3. $(JAVA) includes options, which much be stripped to be a rewrapper toolchain input.

Test: ran against an RBE cluster with RBE_D8_EXEC_STRATEGY=remote and RBE_R8_EXEC_STRATEGY=remote

Change-Id: Icf434f5c0fda687c70c75b01b0bfd63bcd8cc474