* Generate code coverage report
Enable jacoco, the official Gradle code coverage plugin.
The 'build' task will write a code coverage report to
build/reports/jacoco for each subproject that has tests.
We should consider publish periodical reports to a well known
location.
This change also defines a minimum coverage verification task.
The task is for experiment only, and is not added to the build
process yet.
This option causes Intellij build to fail if the
'Delegate IDE build/run actions to gradle' box is checked.
We do not know of anyway to change the Intellij behavior.
This change allows an IDE user to prevent -Werror to be passed
to javac by adding a Gradle VM option: -Dno_werror=true
