Add key split to subtags in ec2.py autodiscover script

[jnerin]

Add the option to create subgroups based on splitting the value of the
key tags by whitespace.

AWS Tag & Value:
"private:app" = "app01 app02 app03 app04 app05 app06"

ec2.py groups:
"tag_private_app_app01": [
"172..."
],
"tag_private_app_app01_app02_app03_app04_app05_____app06": [
"172..."
],
"tag_private_app_app02": [
"172..."
],
"tag_private_app_app03": [
"172..."
],

The idea is to be able to have more fine grained groups like:

• private:app = "list of apps/services the host is running like dns web db cache"
• private:env = "production/staging/testing"

And be able to combine it like:
ansible-playbook --limit 'tag_private_app_cache:&tag_private_env_staging'

[jnerin]

A very similar feature was merged few days later at e6a9b2c