Sets max device connections to number of threads, to a max of 32. Adds V100 to CI.

This MR does two things:

• Sets the number of device connections to the number of threads through the environment variable CUDA_DEVICE_MAX_CONNECTIONS to be equal to the number of threads when launching the application in CUDA device target. The maximum is 32.
• Adds the V100 to the nightly tests.

/ci-test --merge

Started reference and integration test builds. Once done, check the comparison of build and test results.

• [2020-06-18 14:03] Validation started with lhcb-master-mr#958

merged

mentioned in commit f1c11692

added enhancement label