Print test reports in the sbt test-agent

[adpi2]

Bloop writes a final test report at the end of the scalaTestSuites execution:

The sbt test-agent should print a similar test report. The current report is:

Maybe we can use one of the default sbt test listener to do so.

[adpi2]

Some inputs to work on this issue:

• The test suite summary is built here. We can print it using listener.out.
• A test that it is correctly printed out can be added in one of the scripted test, for instance this one, using the Outputed step event.