Support additional build types. (#2033)
Support additional build types. (#2033)

Add support for the additional build types in Travis. These builds can
be moved to Kokoro, but we need to merge these changes first, then
enable them in Kokoro, and then remove them from Travis.

The code coverage build uses Travis-specific scripts, so these changes
do not include them.

googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp,googleapis/google-cloud-cpp