2 changes: flushed userdata scripts. changed constants to env vars

[mpechner-akasa]

https://github.com/aws-samples/amazon-cloudwatch-auto-alarms/pull/39

Description of changes: src/cw_auto_alarms.py Took the following constants: default_period = '5m' default_evaluation_periods = '1' default_statistic = 'Average' Added unique env vars for each: ec2, lambda and rds For instance in my shop, unless RDS CPU is 100% for over 90 minutes, do not care.

Flushed out and used /etc/os-release to make calls OS dependent instead of having to comment or not comment. even if this is meant as an example to put in your own userdata, makes life easier when checking out this tool. userdata_linux_advanced.sh userdata_linux_basic.sh userdata_linux_standard.sh