WFLY-3809 Fix JBOSS_HOME path substitution on Windows.

Given JBOSS_HOME=c:\foo\bar\baz, Windows VirtualFile.getPathName()
returns something like:

/c:/foo/bar/baz

This differs from File.getAbsolutePath() which is used elsewhere in JDR.
This caused an issue where $JBOSS_HOME was not being properly replaced
in the generated archive.