build-unit-test-docker: Replace lcov with gcovr

Resolves openbmc/openbmc-build-scripts#37

Tested: run-unit-test-docker.sh runs correctly and coverage report
generated by gcovr is present

Change-Id: I60134758477cb8f2f5deb94c26eca515d48199f2
Signed-off-by: Ewelina Walkusz <ewelinax.walkusz@intel.com>
1 file changed