Exercises - add scope guards to remove runtime warning messages

[ndellingwood]

Runtime warning messages need to be fixed:

Kokkos allocation "A" is being deallocated after Kokkos::finalize was called
This behavior is incorrect Kokkos usage, and will crash in future releases
Kokkos allocation "x" is being deallocated after Kokkos::finalize was called
This behavior is incorrect Kokkos usage, and will crash in future releases
Kokkos allocation "y" is being deallocated after Kokkos::finalize was called
This behavior is incorrect Kokkos usage, and will crash in future releases

Add scope guards { and } or replace Kokkos::initialize() and Kokkos::finalize() with construction of a Kokkos::ScopeGuard object to address this.

[ndellingwood]

Fixed.