Extract destroy steps from command

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
Extract destroyer spec

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
Short-circuit aws destroy if prod

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>
Remove redundant instance count check

Signed-off-by: Abhijit Hiremagalur <abhi@pivotallabs.com>