Why I did it
To gracefully unmount filesystems and stop containers while performing a cold reboot.
Unmount ONIE-BOOT if mounted during fast/soft/warm reboot
How I did it
Override systemd-reboot service to perform a cold reboot.
Unmount ONIE-BOOT if mounted using fast/soft/warm-reboot plugins.
How to verify it
On reboot, verify that the container stop and filesystem unmount services have completed execution before the platform reboot.
#### Why I did it
- After [sonic-linux-kernel#177](https://github.com/Azure/sonic-linux-kernel/pull/177) changes, the I2C mux channels of Baseboard and Switchboard CPLDs are moved from i2c-4 and i2c-5 to i2c-36 and i2c-37 respectively.
- This caused QSFP driver initialization of i2c-36 to i2c-41 to fail causing the ports from Ethernet208 to Ethernet248 fail.
#### How I did it
- The fix to this problem is to change the order of QSFP driver initialization to I2C mux channels.
- Instead of the order i2c-10 to i2c-41, the order i2c-4 to i2c-35 is being utilized.
- Also, need to change the i2c-mux-channel number for Baseboard CPLD and switchboard CPLD in scripts to access them.
- Dynamically change EEPROM driver based on media type.
- Otherwise, EEPROM INFO and DOM INFO might not be fetched properly and will result in erroneous output.
- Make DellEMC platform modules Python3 compliant.
- Change return type of PSU Platform APIs in DellEMC Z9264, S5232 and Thermal Platform APIs in S5232 to 'float'.
- Remove multiple copies of pcisysfs.py.
- PEP8 style changes for utility scripts.
- Build and install Python3 version of sonic_platform package.
- Fix minor Platform API issues.
