Make sure that AutoScalingGroup depends on the launch config

It seems to be common error to do the following:
  LaunchConfigurationName: my_config
and not include a depends_on.

Largely because of the unfortunate property name.
So this patch tries to make sure the user has the
correct dependency in place.

Change-Id: I4f7d282d0af8681dc2c8cd265e16a27fe23a3bdb
Closes-bug: #1375777
Merge "Make sure that AutoScalingGroup depends on the launch config"