[hloeung] As per config.yaml, fixed so that ssl_key is ignored when ssl_cert is specified as SELFSIGNED.
[hloeung] Added option to provide chain certificates file as a config option.
[hloeung] Fixed PEP8 errors.
Merging MP:153721. Allow config option for providing SSL chain certificates file very much like what we have for certificates and private keys. Also fixed up so that ssl_key is ignored when ssl_cert is specified as SELFSIGNED like what the description in config.yaml says.