the get_elb_list function no longer works properly for retrieving a list of ELBs the instance is currently registered to directly (not in an auto scaling group). The underlying issue was that get_instance_health_elb always returned OutOfService rather than a non-zero exit code when the instance was not registered to the load balancer, because the API returns OutOfService with the description "Instance is not currently registered with the LoadBalancer." (Perhaps this used to return an error but was changed in the API more recently?)

This PR rewrites this function to return the list of load balancers which have the instance in question in their Instances array, rather than querying get_instance_health_elb for each load balancer individually. This also speeds up the function (only requires a single AWS API call versus a separate API call per load balancer).

I used grep and awk instead of the equivalent JMESPath filter expression because old versions of jmespath (my use case is v0.2.1 from the Ubuntu Trusty package) do not support these advanced expressions.