[WFCORE-148] Response stream tests and tweaks

Tests of HTTP client use of the response stream attachment stuff, plus a couple tweaks for stuff I noticed while writing the tests or porting this to EAP.

Kabir: I have merged the EAP counterpart so if there are any problems with this one, let me know. Testing it at http://brontes.lab.eng.brq.redhat.com/viewLog.html?buildId=28839&tab=buildResultsDiv&buildTypeId=WF_WildFlyCoreIntegrationExperiments and