Cleanup runTests a bit (#1992)
Cleanup runTests a bit (#1992)

* move filtering flow versions to own function

* move fetching and filtering out of while loop

* map instead of forEach

* get rid of side-effect based variable assigning

* less indentation by flipping null check

* move flow bin fetching out of runTestGroup

mwalkerwells/flow-typed,doberkofler/flow-typed,flowtype/flow-typed,orlandoc01/flow-typed,splodingsocks/FlowTyped,mwalkerwells/flow-typed,flowtype/flow-typed,doberkofler/flow-typed,splodingsocks/FlowTyped,orlandoc01/flow-typed