DellEMC: Platform2.0 API enhancements in DellEMC S6000 and other API changes

[ArunSaravananBalachandran]

- What I did

• Handle Platform2.0 APIs based on platform driver initialization in DellEMC S6000.
• Fixed _sfp_list, _psu_list , _fan_list initialized to None.
• Return Appropriate values for Fan Direction in DellEMC platforms.

- How I did it

• Made changes to return values based on the driver initialization state in DellEMC S6000.
• Use ChassisBase's init to initialize empty lists for different devices (_sfp_list , _psu_list , _fan_list).

- How to verify it

Wrote a python script to load Chassis class and then call the APIs accordingly.
UT logs - UT_logs.txt
Test Script - platform_test_py.txt

- Description for the changelog

DellEMC: Platform2.0 API enhancements in DellEMC S6000 and other API changes

- A picture of a cute animal (not mandatory but encouraged)

[ArunSaravananBalachandran]

This PR needs to be picked for 201911 branch, after PR3740 has been ported to 201911 branch.

[jleveque]

Retest this please

[ArunSaravananBalachandran]

retest mellanox please

[ArunSaravananBalachandran]

retest vsimage please

[lguohan]

retest vsimage please

[jleveque]

@ArunSaravananBalachandran: Has #3740 been ported to the 201911 branch? I will wait to merge this until it has, because once this gets merged to master, it will get cherry-picked to 201911 shortly.

[ArunSaravananBalachandran]

@ArunSaravananBalachandran: Has #3740 been ported to the 201911 branch? I will wait to merge this until it has, because once this gets merged to master, it will get cherry-picked to 201911 shortly.

@jleveque PR3740 can be directly cherry-picked to 201911 branch.

[jleveque]

@ArunSaravananBalachandran: Thanks for the info. I have added a label to that PR so that it gets cherry-picked into 201911.