Consider building/watching key WebPageTest ecosystem projects

To help ensure our use-cases in the larger WebPageTest ecosystem are healthy, we probably want to consider something like the following:

• build latest (master) from: ** webpagetest ** wptagent ** webpagetest-api [do something meaningful for us/upstream, if any of these fail?]

All have both Docker and Travis CI builds, which should make this easier -- we should vet those too, though, carefully.

/cc @soulgalore @davehunt

https://www.webpagetest.org/result/181210_BC_aea494720118d71fb12ed9cd10c552ac/