Lie about the value of java.version

At runtime on android the 'java.version' property has the value '0'.
Accurately reporting this value through the VirtualMachine.version
function can cause some debugger clients to become confused. To fix
this we will lie and return '8' instead in the function.

Test: examine JDWP packets
Test: ./art/tools/run-libjdwp-tests.sh --mode=host
Bug: 116255327
Change-Id: I0cd188b9cb6b55b9a1509804bff79c3ba5995feb