Incorporate a modified form of Martynas Jusevicius's patch for JENA-405

QueryEngineHTTP now respects service context if one has been configured for the specified remote service.  Adds additional tests to TestService to check that configuration is respected

git-svn-id: https://svn.apache.org/repos/asf/jena/trunk@1462623 13f79535-47bb-0310-9956-ffa450edef68