Change hawkular.rest.host to hawkular.rest.url

In https://github.com/hawkular/hawkular-agent/blob/master/hawkular-javaagent-wildfly-feature-pack/src/main/resources/featurepack/content/standalone/configuration/hawkular-javaagent-config.yaml#L36 we are using the parameter name 'hawkular.rest.host' when this is not specifying a hostname but a url.

We should rename this to something more accurate (such as hawkular.rest.url)