Check device count before running dist tests (#2799)
* Check device count before running dist tests
* fixing format for "Check device count before running dist tests"
* Check device count against max world size
* Check GPU count before launching dist tests
* double-check GPU actually exists
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Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>
Co-authored-by: Jeff Rasley <jerasley@microsoft.com>
Co-authored-by: Michael Wyatt <michaelwyatt@microsoft.com>
