service.bat script add support for environment variables

Hello,

I'm using wildly as my application server. To provide customizable configuration I want to use STANDALONE_CONF environement variable.

This works fine with stanalone.bat but when I try to install wildfly as a service I can't set this environment variable to service.bat.

I wrote an unpdate to service.bat to handle environment variables.

Can I make a pull request on github?

Best regards