Description of problem:
When running many (>100) hosts on FakeVDSM with JSON communication, a JSON command is roughly 400 times slower than a similar XML command

Version-Release number of selected component (if applicable):
3.5

How reproducible:


Steps to Reproduce:
1. Create >100 hosts in engine
2. Direct them to FakeVDSM
3. Configure hosts to use JSON instead of XML1.
4. Use a profiler to measure the performance of JsonRpcVdsServer.getVdsStats vs. VdsServerWrapper.getVdsStats 

Actual results:
>1s per execution

Expected results:
~20ms per execution

Additional info: