boto_elb alarms and attributes from pillars

Take attributes and cloudwatch alarm values from pillars. attributes
can come from a custom defined pillar key, or if undefined from a default
pillar key 'boto_elb_attributes'. Alarms can also come from a custom
defined pillar key, or if undefined from a default key 'boto_elb_alarms'.
Add documentation for alarms, alarms_from_pillar and attributes_from_pillar
Add note about alarm name
Merge pull request #19233 from lyft/elb-args-from-pillar

Elb args from pillar