* Adds scripts to generate scale sets for testing Linux.
* Note workaround for https://github.com/microsoft/azure-pipelines-agent/pull/2929
* Switches Windows validation to 'Spot' VMs.
* Opens the git port 9418.
* Removes provisioning of the no longer used 'logs' file share.
* Changes Azure region to 'westus2', which is cheaper.
* Adds +x to all the scripts in scripts/azure-pipelines.
* Use 'xml-results' for all platforms instead of 'raw xml results' on Windows.
