Update Wmi and IisVirtualDirectory code to accept username and password

I've been trying to get dropkick setup to run as a step in a TeamCity build, to deploy from one Amazon VM to another.  The VMs are not in the same domain, so the user on the build server does not have any administrative rights on the target server, so we needed to be able to pass in an administrative username and password to open the WMI connection.

This creates a new WithAdministratorAccount method on IisVirtualDirectoryOptions, and passes that username and password all they down to WmiHelper.