HttpManagement interface json.pretty=1 fails

Don't work on this
(This is a deliberate regression of https://issues.jboss.org/browse/WFLY-3371 which will be introduced for a few hours on Tuesday 21st April 2015, so I have something to fix during a JBug demo)

When attempting to call e.g. http://localhost:9990/management/subsystem/jmx?json.pretty=1

an IllegalStateException happens. Debugging shows this to happen on the following line of DomainApiHandler

operationParameterBuilder.pretty(dmr.hasDefined("json.pretty") && dmr.get("json.pretty").asBoolean());

The dmr access needs to take into account that the parameter is not necessarily a boolen.