Leave the check for Standard sku during slot creation on server side. Fix the webspace to the the webspace of prod slot.
Error message durign creation of slot on Free site is New-AzureWebsite : Conflict: Cannot complete the operation because the site will exceed the number of slots allowed for the 'Free' SKU.
Merge pull request #3061 from galcho/release-0.8.11

Leave the check for Standard sku during slot creation on server side.