Updates to the CI triggers:
- Stop running parallel CI runs, i.e. if a pipeline is running, it must finish before new runs are started.
- Exclude paths to files, which are not related to/critical the codebase
- Downloading MKL from a mirror hosting server
This PR adds an Azure Pipeline for running regression tests on an Azure Hosted GPU Pool.
It currently run on Ubuntu 18.04, GCC 8, CUDA 11.1, a single Nvidia M60 GPU device (Maxwell).
The pipeline needs to be started manually: go to "Pipelines", then "Marian GPU Pool", click "Run pipeline", select the branch, click "Run".
