Azure plugin: allow CNAMEs with 'https' via filter
Azure plugin: allow CNAMEs with 'https' via filter

If a CNAME is set with 'https', silently rewrite to 'http' since 'https'
isn't supported by Azure Storage.

This change introduces a new private utility method and the
'windows_azure_storage_allow_cname_https' filter to use with it.

mrgregwaugh/windows-azure-storage,mrgregwaugh/windows-azure-storage