jsonrpc: Federate context and request-response objects

This is the ground work needed to allow batch requests and bidirectional
jsonrpc.

Change-Id: I091ca9acad5940418cbf3961a76a06cbfef976f0
Signed-off-by: Saggi Mizrahi <smizrahi@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/10375
Reviewed-by: Adam Litke <agl@us.ibm.com>
Tested-by: Adam Litke <agl@us.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>