Updated the security_group attribute to use a set

This way the order returned by the API has no impact on the saved
state, preventing false positives when diffing.
Merge pull request #690 from svanharmelen/f-provider/aws-fix-elb-resource

provider/aws: updated the security_group attribute to use a set
Changing this fixes an Excoscale issue where 'all' is not allowed
Merge pull request #699 from svanharmelen/f-provider/cloudstack-small-fix

provider/cloudstack: changing this fixes an Excoscale issue where 'all' is not allowed