Improvement: check db connection before starting the install process

[enfJoao]

If I type the sql server instance name wrong, it will create the site in the list (and the folders), but fail with a non specific folder error.

If I go back to the site list and try to remove the site, it will fail while trying to remove the database. There was no database created, but it doesn't know that because of the bad instance name.

[david-poindexter]

@enfJoao thank you for this issue. We agree this could be a candidate for improvement.