Azure/Kubernetes: contributed to Azure/azure-powershell

This was not the greatest contribution to the azure-powershell Git repository, https://github.com/jdnark/azure-powershell. The PR below fixes four instances of the same typo (changed SshKeyVaule to SshKeyValue) which manifests itself in the New-AzAksCluster cmdlet where a duplicate or missing SSH key is detected: