Make the language and dist/os Travis options useful

The Travis file has options for the language and either os or dist to use. It would be good for people to be able to utilize these and Buildbot to map those options to whatever needed internally to effect what is expected. It is unclear to me at the moment if the os or dist option is the correct one to use. I am going to use os from now on for simplicity.

As an example, if using Docker, the os option could point to a higher-level option such as "trusty" or "xenial" and then Buildbot would map that to what the Docker worker needs in order to use a container for that OS. I think if an unknown option is used, the build for that OS should not be triggered and instead fail.

A similar thing for the language. There could be variants for the OS that include packages specific for that language so the basic tools do not have to be installed.