Thread safe initialization of dummy PSet static in HLTConfigData

Modified the code to safely initialize the registration of the dummy
PSet static used in HLTConfigData. Also avoid having the registration
call make each time the function was called.
This was spotted by the static analyzer.
Merge pull request #4423 from Dr15Jones/safeInitOfStaticHLTConfigData

Thread safe initialization of dummy PSet static in HLTConfigData