[Juniper][QFX5200] EM policy updates (#4543)

This patchset implement the following:
 - Setting the FAN frequency
 - Corrections to the EM policy with respect to platform
   defined temperature / fan values
 - Updates to the platform monitorng script logging
 - Fixes to platform initialization script

Signed-off-by: Ciju Rajan K <crajank@juniper.net>

Author: ciju-juniper