[Mellanox] Refactor Mellanox platform API to support dynamic port con…

…figuration (#8422)

- Why I did it
* To support systems with dynamic port configuration
* Apply lazy initialization to faster the speed of loading platform API

- How I did it
* Add module.py to implement dynamic port configuration (aka line card model)
* Adjust chassis.py, platform.py, thermal.py, sfp.py to support dynamic port configuration
* Optimize existing code

- How to verify it
Platform regression on MSN4700, MSN3800 and MSN2700, 100% pass
Unit test covers all new changes.

.gitignore

@@ -83,6 +83,13 @@ dockers/**/buildinfo
 platform/**/buildinfo
 sonic-slave*/**/buildinfo
 
+# pytest coverage files
+.coverage
+coverage.xml
+test-results.xml
+htmlcov/
+
 # Dev tools
 .vscode/
 .idea/
+

platform/mellanox/mlnx-platform-api/.gitignore

@@ -1,2 +1,6 @@
 *.pyc
 .cache/
+*/test-results.xml
+*/htmlcov/
+*/coverage.xml
+*/.coverage

platform/mellanox/mlnx-platform-api/pytest.ini

@@ -15,5 +15,6 @@
 ## limitations under the License.
 ##
 [pytest]
+addopts = --cov=sonic_platform --cov-report html --cov-report term --cov-report xml --junitxml=test-results.xml -vv
 filterwarnings =
     ignore::DeprecationWarning