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:
http://docs.aws.amazon.com/Route53/latest/APIReference/actions-on-zones-private.html
Add Check privateZone == false to create_hosted_zone unit test
Fixing comparison for PrivateZone test
committing for the night. test is currently failing
fix previous test, add test to make sure 400 is returned
Change from camelcase to underscore to keep with convention
add integration test for creating a private zone
clean up private zone test
Merge pull request #1 from Twistedpear/privatezone

Privatezone: Adding unit/integration test coverage
update private zone tests to work with changed vpc_id and vpc_region variable names
Add to documentation/usage comment
Shorten long lines
Shortened more lines
Shorten more lines
Shortened a few more lines in test files
Merge pull request #2785 from djcross/privatezone

Add support for private hosted zones. Fixes #2785.