More direct configuration for jobs in Travis build

[marcospereira]

• Not using multiple scripts to run tests
• More consistent with other samples we maintain (such as Play)

[ignasi35]

Travis downloads have broken a couple of jobs with corrupted jars causing compilation or runtime errors. I've relaunched them.

Coincidentally, it was the Java-11 - Lagom gRPC {scala,java} jobs so at first, it looked like another cause.

[marcospereira]

It is all green now. Are you okay with these changes?

[marcospereira]

@ignasi35 I'm merging this myself since you approved the other two that depend on this.

We can always adjust the build later too.

Thanks. :-)

[ignasi35]

Merge! :all-the-things: :-)