Merged in barry/cuda-multigrid-test (pull request #1763)

Various improvements for GPUs (mostly for performance and CUDA)

Added PetscCUDAInitialize() which the user may call in the body of the program, -cuda_initialize 0 prevents PetscInitialize() from initializing CUDA

Add -cuda_initialize 0 as options database for CU

Added PetscCUDAInitialize() which the user may call in the body of the program, -cuda_initialize 0 prevents PetscInitialize() from initializing CUDA

Add -cuda_initialize 0 as options database for CUDA tests so machines won't load cuBLAS unless actually
utilizing it on the machine, update examples to filter option-cuda_initialize

Reported-by: Karl Rupp <me@karlrupp.net>
Commit-type: feature

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