Improve error handling in synchronous command invokation (OMS-545)
Improve error handling in HTTP REST command execution: always catch exceptions and cancel processing if connection is lost (OMS-545)
Use HTTP code 500 instead of (wrong) 408 (OMS-545)
Use HTTP code 504 instead of the vague 500 (OMS-545)
Merge pull request #208 from opennode/oms-545

Improve error handling in synchronous command invocation (OMS-545)