ConfigInstructions should throw an exception when DependsOn points to itself

[alx9r]

Consider the following:

$document = {
    Get-DscResource TestStub | Import-DscResource

    TestStub a @{
        Key = 'a'
        DependsOn = '[TestStub]a'
    }
}

$instructions = ConfigInstructions Name $document

[TestStub]a depends on itself. I can't see any meaning to a normal resource depending on itself. A normal resource depending on itself almost certainly indicates a user error. Processing of [TestStub]a should throw an exception because it points to itself.

It's worth noting that an aggregate resource could depend on itself because it could count itself in whatever aggregation logic it is applying.

A test for this behavior is already mentioned in configDocumentType.Tests.ps1.