RFR(XS): 8169734: Update uses of string "java.base" to macro

[Rachel Protacio]

Hi!

Please review this little change, replacing errant uses of the string 
"java.base" with the macro JAVA_BASE_NAME. Passes JPRT.

Bug: https://bugs.openjdk.java.net/browse/JDK-8169734
Open webrev: http://cr.openjdk.java.net/~rprotacio/8169734.00/

Thanks,
Rachel