Smooth out potential issues using ResetDevSite

[bdukes]

Summary

This PR resolves two issues we ran into while using ResetDevSite to setup a new DNN dev site (plus a third issue that I thought about while in the code).

DatabasePath Normalization

The first issue is that you get an obscure SQL error if the DatabasePath in your local settings uses / instead of \ (or, really \\ since it's a JSON file).

========================================
ResetDatabase
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System.Data.SqlClient.SqlException (0x80131904): A file activation error occurred. The physical file name 'C:/dbs/dnn.local\dnn.local.mdf' may be incorrect. Diagnose and correct additional errors, and retry the operation.
CREATE DATABASE failed. Some file names listed could not be created. Check related errors.

DatabasePath Creation

The extra issue is that if DatabasePath doesn't already exist you get the following error:

========================================
ResetDatabase
========================================
System.Data.SqlClient.SqlException (0x80131904): Directory lookup for the file "C:\dbs\dnn.local\dnn.local.mdf" failed with the operating system error 3(The system cannot find the path specified.).
CREATE DATABASE failed. Some file names listed could not be created. Check related errors.

Blank DnnConnectionString

The final issue we ran into was leaving DnnConnectionString blank and then getting a Yellow Screen of Death when the web.config was updated with the blank value. I added a check and throw an error if you're trying to set the web.config with a blank connection string.

[david-poindexter]

Nice enhancements @bdukes 🎉

[donker]

Thanks!