Remove default empty value

[pagmerek]

what

• Remove default null field in mixed instances policy

why

According to terraform docs:

An optional attribute with a non-null default value is guaranteed to never have the value null within the receiving module. 
Terraform will substitute the default value both when a caller omits the attribute altogether and when a caller explicitly
sets it to null, thereby avoiding the need for additional checks to handle a possible null value. 

In ASG Cloudposse component here you can see that on any value that is not null it will create mixed_instances_policy

references

• related PR in ASG component: Change mixed instances policy fields to optional terraform-aws-ec2-autoscale-group#126

[goruha]

/terratest

[goruha]

/terratest

[goruha]

/terratest