RFR: JDK-8223325: Improve wix sources generated by jpackage

[Alexey Semenyuk]

Please review the jpackage fix for bug [1] at [2].

This is a fix for the JDK-8200758-branch branch of the open sandbox 
repository (jpackage).

- moved code creating WiX sources for app image from WinMsiBundler in a 
separate class - WixSourcesBuilder;
- put at most one file in component in WiX sources;
- use StAX to create WiX sources;
- added IOUtils.createXml function to simplify xml creation;
- added basic javadoc to AppImageFile class;
- added support for use of icons in file associations test for better 
coverage;
- fixed the bug with not excluded `.jpackage.xml` from installed app 
image on Windows;
- improved test output isolation when jpackage tests are executed not 
with jtreg framework;
- bugfix of MainClassTest test class;

- Alexey

[1] https://bugs.openjdk.java.net/browse/JDK-8223325

[2] http://cr.openjdk.java.net/~asemenyuk/8223325/webrev.00/