`files.h/files.cpp`:
* Add end and else comments to all macros.
* Add "remove_all_inside" function which empties a directory without actually deleting the directory. This is necessary to handle the case where the directory is actually a directory symlink.
* Change remove_all to use std::remove when VCPKG_USE_STD_FILESYSTEM is set; this will engage POSIX delete support available on current Win10.
`commands.ci.cpp`: empty "installed".
`*/initialize_environment.*`: No longer clean the directories outside the tool.
`ci-step.ps1`: Remove unused console output tee-ing.
* 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.
