Ensure newly created NAT gateways get converted to snake dict
Remove custom code, and associated test, for generating snake
dict and use `camel_dict_to_snake_dict`
Make use of `required_if` rather than bespoke parameter checks
Remove ec2_vpc_nat_gateway from pep8 legacy files list
Changes to the metadata format were approved here:
https://github.com/ansible/proposals/issues/54
* Update documentation to the new metadata format
* Changes to metadata-tool to account for new metadata
* Add GPL license header
* Add upgrade subcommand to upgrade metadata version
* Change default metadata to the new format
* Fix exclusion of non-modules from the metadata report
* Fix ansible-doc for new module metadata
* Exclude metadata version from ansible-doc output
* Fix website docs generation for the new metadata
* Update metadata schema in valiate-modules test
* Update the metadata in all modules to the new version
* Update validate-modules
* Validates ANSIBLE_METADATA
* Ensures imports happen after documentation vars
* Some pep8 cleanup
* Clean up some left over unneeded code
* Update modules for new module guidelines and validate-modules checks
* Update imports for ec2_vpc_route_table and ec2_vpc_nat_gateway
* Check if EIP exists before deleting it
After deleting the NAT gateway, the EIP sometimes seems to
cease to exist afterwards. Check if it exists before deleting it.
Otherwise you get:
```
Failed to release EIP eipalloc-abdc1234: An error occurred (InvalidAllocationID.NotFound) \
when calling the ReleaseAddress operation: The allocation ID 'eipalloc-abcd1234' does not \
exist", "success": false}
```
* Fix flake8 errors with ec2_vpc_nat_gateway