What I did

1. Support to dump the gcda files in the each of docker-sonic-vs containers when running the tests of sonic-swss.
2. Support to collect the coverage in the cobertura format directly from the sonic-swss build and the docker-sonic-vs containers during the component tests.
3. Simply the logic to collect the coverage. Use the dotnet tool reportgenerator to merge all the coverage files in cobertura format.
4. Reduce build time using the sonicbld agent pool (36 minutes -> 20 minutes), reduce test time by running the tests in parallel (8 pytest processes) and using more powerful agent pool sonic-common-test (4hours -> 1 hours).
5. Improve the test stability, retry 3 times if failed.

Why I did it
Fix the coverage issue, some of the files are not covered in the coverage report.
Reduce the build/test time.

How I verified it
see the full coverage page in the build result.

Details if related

1. __gcov_flush removed in GCC11, changed to use gcov_dump, see https://gcc.gnu.org/onlinedocs/gcc/Gcov-and-Optimization.html. The gcov shared library does not work as expected, changed to link the gcov ctor in the programs directly.
2. Add the --enable-coverage option in the conftest.py to collect the coverage.
3. Add a test utility tests/run-tests.py to run the test module with retry.
4. Change gcovpreload.c to gcovpreload.cpp, some of the gcc options are not supported if using the suffix xxxx.c, such as -std=c++14, -Wno-reorder.