[cuda] lavaMD and mandel are flaky

• Failing: test-cuda-debug, test-cuda-release
• Passing: test-cuda-debug, test-cuda-release

The failures look like this:

14/35 Test #26: lavaMD ...........................***Exception: Other  1.44 sec
lavaMD: /builds/HPC2SE-Project/pacxx-samples/llvm/include/llvm/IR/Instructions.h:830: llvm::Type* llvm::checkGEPType(llvm::Type*): Assertion `Ty && "Invalid GetElementPtrInst indices for type!"' failed.
WG size of kernel = 128 
Configuration used: arch = 0, cores = 1, boxes1d = 10

20/35 Test #11: mandel ...........................***Exception: Numerical  2.36 sec
Distance: 16777216
Declaring lambda
Launching