Please review a simple localized fix to construct the System Properties page using the recently-new standard flex-box layout.
For reference, the modified code was based on equivalent code in SingleIndexWriter.generateIndexFile.
The existing test for the page is extended with additional checks for the new behavior.
-- Jon JBS: https://bugs.openjdk.java.net/browse/JDK-8240476 Webrev: http://cr.openjdk.java.net/~jjg/8240476/webrev.00/index.html
