appveyor.yml: publish test results

- Recent change at AppVeyor parses our NUnit output
- Publishes test NUnit results to the build's Tests tab
- Also:
  * make Configuration a parameter rather than hard wired
  * set DLR_ROOT and DLR_BIN
  * use defaults for email content

Signed-off-by: Tim Orling <timothy.t.orling@linux.intel.com>