Add support for private hosted zones

Utilising the existing create_zone and create_hosted_zone functions,
create a private zone by using the new arguments:
private_zone=True, VPCId='<vpcid>', VPCRegion='<region>'

Tested locally to not break current functionality

AWS API documentation on private hosted zones:
private_zone=True, VPCId='vpc-2403f141', VPCRegion='ap-southeast-2