Add environment information to each execution of tests in the tSQLt build validation step.

[mbt1]

We encountered an issue (randomly failing EXECUTE AS) that seems to be caused by a change to the operating system, not to SQL Server. As we have not yet been tracking that information, there's no way to know for sure. Let's fix this for the next time.

This query provides a start as to what to include:

SELECT * 
  FROM sys.dm_os_sys_info AS DOSI
  CROSS JOIN sys.dm_os_host_info AS DOHI
    FOR XML PATH(''),TYPE

The output should be printed at the beginning of each call to tSQLt.RunNew (not just at the beginning of each run of the build).