Added Fog::AWS::SES.verify_domain_identity.

* http://docs.aws.amazon.com/ses/latest/APIReference/API_VerifyDomainIdentity.html
* Added Fog::Parsers::AWS::SES::VerifyDomainIdentity.
Fixed description for the #verify_domain_identity tests.
Actually call verify_domain_identity.
Signature method requires x-amz-security-token header.
Merge pull request #1940 from adamjt/fix_s3_request_signing

Signature method requires x-amz-security-token header.
Merge pull request #1926 from postmodern/aws_ses_verify_domain

Added Fog::AWS::SES.verify_domain_identity.