check-https-cert.rb does not expose "verify_depth" for validating full certificate chain

[brubin86]

See similar PR for sensu-plugins-ssl: sensu-plugins/sensu-plugins-ssl#66

A flag to set "verify_depth" on the http instance would allow users to indicate they prefer checking parts of the certificate chain above just the leaf certificate:

https://github.com/sensu-plugins/sensu-plugins-http/blob/master/bin/check-https-cert.rb#L89