xWebAdministration: Stubs for unit tests should throw if they are called

[johlju]

When the stubs are called, they are executed and nothing happens. They should instead throw an error saying that Stub was called. This way it is shown that a cmdlet wasn't mocked correctly. If cmdlets are not mocked correctly then when user expecting to run unit tests on a lab it could actually change the system that only an integration test should do.

All stub functions here:
https://github.com/PowerShell/xWebAdministration/blob/dev/Tests/MockWebAdministrationWindowsFeature.psm1

Should throw something like this.

throw '{0}: StubNotImplemented' -f $MyInvocation.MyCommand