[build] Add a test coverage report to the Java build

This patch adds a jacoco test coverage report to the Java build.
The report can be generated by running
`./gradlew jacocoAggregatedReport` and looking at
`java/build/reports/jacoco/jacocoAggregatedReport/html/index.html`

A follow on patch will add this coverage run to the build-and-test.sh
“COVERAGE” type build.

Change-Id: I0f2a2b1836b5ade72a757a8d7e2c518858ec48bb
Reviewed-on: http://gerrit.cloudera.org:8080/16954
Tested-by: Kudu Jenkins
Reviewed-by: Alexey Serbin <aserbin@cloudera.com>
4 files changed