Add code coverage for framework tests
This patch adds code coverage for framework unit tests. The
output information can be found under <BUILD_DIR>/framework/test.
To avoid collisions between framework test code coverage and
module test code coverage, the output directory for module tests
is changed to <BUILD_DIR>/module/unit_test instead of <BUILD_DIR>.
A new ENABLE_COVERAGE flag to the Makefile
wrapper, allowing for conditional generation of code coverage reports
for fwk_test and mod_test targets