Allow managerUrl (or manager contextPath) to be configured in remote 6 container

Tomcat 7 changed the context path for the manager apps. For the purpose of what the Arquillian adapter uses, the context path changed from /manager to /manager/text.

Unfortunately, the tomcat adapter does not provide a way to configure the context path of the manager url. It builds it automatically as follows:

protected URL createManagerUrl() throws MalformedURLException
{
    final String template = "http://%s:%d/manager";
    return new URL(String.format(template, bindAddress, bindHttpPort));
}

At a minimum, we should add a new property "managerContextPath" and honor that in this method.

Better would be to also allow the managerUrl to be overridden entirely. This currently does not work because

1. arquillian cannot convert a configuration property to a URL
2. even if it did, the value is overridden in the validate() method anyway

This fix will allow the Tomcat 6 remote adapter to work with Tomcat 7.

Side note:

The user should also be advised that it is necessary to include the JMX startup properties when starting Tomcat 7.

-Dcom.sun.management.jmxremote.port=8089 -Dcom.sun.management.jmxremote.ssl=false -Dcom.sun.management.jmxremote.authenticate=false