* [Mellanox/mlnx-platform-api] enable mellanox's platform-api to be loaded as a whole.
* [chassis] update reboot-cause handling code to adapt the hw-management currently running on 201811
* [chassis]handle the case that reboot cause file can be any dir matching pattern "hwmonX".
* backport new platform api to 201811, reboot cause part
* install new platform api on host
* 1. remove chassis's dependency on sonic_platform_daemon.
2. add some mellanox-specific hardware reboot causes.
3. fix typo in files/image_config/process-reboot-cause/process-reboot-cause.
* 1. add dependency of sonic_platform for base image
2. handle the case of reboot cause file not found
* adjust log message.
