- remove hard-coded `$(AppRuntimeVersion)` property entirely
- use `$(SharedFxVersion)` instead
nits:
- make `RunTests` help more clear about how `--runtime` option is used
- remove unused `--sdk` option on `RunTests` command line
- add Microsoft.AspNetCore.App.Ref package to Helix content later, ensuring it exists
* Add Windows 7 and 8.1 testing on Helix
* Install SQL Server on-demand in Helix test queues
* Only install mssql on Windows runs
* Use exit /b
* Add targets to better support running helix locally
* Set maxretrycount to 2
* Handle IIS issues on win7/win8
* Make HelixPreCommand's fail the workitem
* Add a pre-generated test cert of IIS Express
* Update helix doc and ignore netsh script failures
* Fix bug in detecting Windows queues and disable Win 7 until we have queues ready
* Fix HttpSys functional tests on Helix