ITW windows launcher registry support

[Alex Kashchenko]

Hi,

This patch ( 
http://cr.openjdk.java.net/~akasko/itw/bat_launcher_20170518.patch ) 
adds registry support for finding out JAVA_HOME to javaws bat launcher. 
JAVA_HOME from environment is used as a fallback. I suggest using it in 
current form until native launcher is implemented.

Tested with default MSI installations of ojdkbuild and Zulu.

-- 
-Alex