Function triggered `PeriodicEvent` does not work properly in parallel

[jafranc]

Describe the bug When set-up like this on a central region c2

    <PeriodicEvent
      name="ConditionalDump"
            logLevel="2"
            maxEventDt="0.1"
            function="sg"
            threshold="0.1"
            object="/Problem/domain.../region2/elementSubRegions/c2"
            stat="0" // min
            target="/Outputs/vtkOutput"/>

in an adaptation of buckleyLeverett_base the min and average seems to be missing in parallel. The max (resp. option stat="2") return 1e10.

There is few adjustment to be made both in PeriodicEvent and FunctionBase to correct the behavior (see #3147)