test: organize test files by resource type.
ec2: rough support for AWS::EC2::NetworkAclEntry.
ec2: add AWS::EC2::NetworkInterfaceAttachment.
ec2: add AWS::EC2::VolumeAttachment.
ec2: add AWS::EC2::VPCPeeringConnection + tests.
ec2: support AWS::EC2::VPCDHCPOptionsAssociation.
ec2: add AWS::EC2::VPNConnection + test.
ec2: add AWS::EC2::VPNConnectionRoute + test.
ec2: add AWS::EC2::VPNGatewayRoutePropagation.