Does a cloud service like Azure or EC2 exist which can run arbitrary workloads? (e.g. Client SKUs of Windows)
Try CloudSigma, Defiantly can upload your own ISO's and run any x86 and 64bit OS you like on it. They have their in-house versions to get started but you can bring your own OS versions.
Based in Switzerland but they would have also the servers in the US, performance i've expected to quite good.https://www.cloudsigma.com/
There is also a free trail on at the moment
https://cs.cloudsigma.com/accounts/signup/
The list of Open Virtualization Alliance members may have some candidates for you.
A search on the page for "operating system" suggests the following possibilities (in addition to the already-mentioned CloudSigma):
- ElasticHosts
- stepping stone GmbH (I'm less sure about this one)
- Sublime IP
No, commercial cloud services like Azure and Amazon EC2 are themselves virtual, so you don't get a great deal of control over the operating system.
An option may be to consider renting a full physical server (colocated, or managed) and then use a battery of virtual machines to run the tests. Something like VMWare's snapshot feature sounds perfect: spin up a clean virtual machine, deploy the test code, then throw away changes to the disk once the tests have been completed.
Or, indeed, as @Stuart suggests - run the tests locally.