Update drivers in perf_tests/graph to use Kokkos::initialize()

[william76]

Motivation

@crtrott requested this on PR #198 but this fix is out of the scope of that PR, which specifically addresses two bugs in the D2 Graph Coloring kernel when run on GPUs, so we should address these changes as an issue and apply the update to all the drivers in perf_test/graph.

We should have a discussion about this fix as well to make sure that using Kokkos::initialize() does what we want it to do for the purposes of the perf tests.

Action Items

Update the drivers in perf_test/graph/ to use Kokkos::initialize() and remove calls like #if defined(KOKKOS_HAVE_OPENMP) in favor of the new system.

Some documentation on Kokkos::initialize() is provided on the Kokkos Wiki.

@mndevec
@crtrott