[201911] DellEMC: Skip thermalctld and thermal platform API changes

[ArunSaravananBalachandran]

- Why I did it

• Skip thermalctld in DellEMC S6000, S6100, Z9100 and Z9264 platforms.
• Change the return type of thermal Platform APIs in DellEMC S6000, S6100 and Z9100 platforms to 'float'.

- How I did it

• Add 'skip_thermalctld:true' in pmon_daemon_control.json for DellEMC S6000, S6100, Z9100 and Z9264 platforms.
• Made changes in thermal.py, for 'get_temperature', 'get_high_threshold' and 'get_low_threshold' to return 'float' value.

- How to verify it

• Check thermalctld is not running in 'pmon'.
• Wrote a python script to load Chassis class and then call the APIs accordingly and verify the return type.

UT Logs: UT_logs.txt
Test Script : thermal_test_py.txt

- Description for the changelog

[201911] DellEMC: Skip thermalctld and thermal platform API changes

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