This patch moves all default settings from the code
to the default single settings file. And modifies
recently introduced settings manager to be able to
also update default values from /etc/fuel/client/config.yaml
file and from environment varables
DocImpact
Blueprint: re-thinking-fuel-client
Change-Id: Ib73b0494cf30e75099aa7a0552745cd4adc3a07e
1ae57d6781