RFR: 8190003: Special characters in group names should be escaped

[Jonathan Gibbons]

Please review this simple fix to better handle the "group name" supplied 
in a -group option.
The name is currently just wrapped in a RawHtml node; it should be 
wrapped in a StringContent node.

JBS: https://bugs.openjdk.java.net/browse/JDK-8190003
Webrev: http://cr.openjdk.java.net/~jjg/8190003/webrev.00/
-- Jon