Default is set to 300 seconds, which is AWS default.

This PR fixes a bug (#7898) where instances created within an autoscaling group using the `ec2_asg` module gets immediately terminated because the `health_check_period` is set to 0, which causes the instance to be checked without having the time to actually boot.

Adding `health_check_type` is needed because you may want to check your instance health against an ELB instead of just EC2 default cloudwatch.