…#154)

- Refactor psud such that the `run()` method does not contain an infinite loop, thus allowing us to unit test it
- Refactor mock_platform.py such that it inherits from sonic-platform-common in order to ensure it is aligned with the current API definitions (this introduces a test-time dependency on the sonic-platform-common package)
- Eliminate the need to check for a `PSUD_UNIT_TESTING` environment variable in daemon code
- Increase overall unit test unit test coverage from 78% to 97%

 Update transceiver info DB key names (sonic-net#146)
[Multiasic]: Provide namespace support for ipNetToMediaPhysAddress (sonic-net#129)
[LLDP]: Modify OID index of LLDPRemTableUpdater MIB (sonic-net#155)
[Namespace]: Simplify sync_d functions to use higher order (sonic-net#154)
[Namespace]: Fix interface counters in RFC 1213 (sonic-net#145)

Signed-off-by: Abhishek Dosi <abdosi@microsoft.com>

When build python3 xcvrd, it tries to do basic check which will import this y_cable.py. However, not all platform supports python3 API now, so it could cause an issue when importing sonic_platform.platform

We skip the ImportError here to make the builder happy. And this is safe because:
- If any python package is not available, there will be exception when use it
- Vendors know their platform API version, they are responsible to use correct python version when importing this file.