setOutputPosition() -> parentOutputPositionChanged()

This function (on both FEProblem and Executioner) no longer sets the
output position, it just calls parentOutputPositionChanged(), so it no
longer needs to take a Point, and I'm changing the name in both
FEProblem and Executioner.

Refs #2912.
Merge pull request #2913 from jwpeterson/set_output_position

setOutputPosition() -> parentOutputPositionChanged()