Tpetra: Replace Tpetra_DefaultNode CMake option with Tpetra_DefaultExecutionSpace
Created by: mhoemmen
@trilinos/tpetra @rppawlo @crtrott
Tpetra will get rid of Node altogether at some point, and tie itself completely to Kokkos' execution and memory spaces. It would make sense to deprecate the Tpetra_DefaultNode CMake option and replace it with Tpetra_DefaultExecutionSpace.