DPDK code coverage reports dashboard page

[Patrick Robb]

Hi DPDK Developers,

I wanted to announce to the mailing lists that the UNH Community Lab
recently rolled out a new page on our dashboard where you can find
code coverage reports for DPDK unit tests.

https://lab.dpdk.org/results/dashboard/code-coverage

It provides some unit test code coverage reports for lib/* and
drivers/*. You can download and extract the test coverage artifacts,
and open up the styled html page by navigating to
out/coveragereport/index.html.

We run these coverage reports 1x/month, on the first day of the month.
Ideally these can serve as a reference for how many lines of code are
touched by unit tests, but also how coverage evolves over time.

Some improvements we have in queue:
    -Add driver-tests and perf-tests testsuites. Currently we are only
running fast-tests and a few individual testcases from driver-tests.
    -embed the test report (with styling) in the lab dashboard page,
so people don't have to download and open the page locally.

We are building gcov/lcov targets according to the documentation here:
https://mesonbuild.com/Unit-tests.html

Questions or suggestions on how to improve the coverage reports are welcome.

Thanks,
-DPDK Community Lab team