* govendor: update go-cloudstack dependency
* Separate security groups and rules
This commit separates the creation and management of security groups and security group rules.
It extends the `icmp` options so you can supply `icmp_type` and `icmp_code` to enbale more specific configs.
And it adds lifecycle management of security group rules, so that security groups do not have to be recreated when rules are added or removed.
This is particulary helpful since the `cloudstack_instance` cannot update a security group without having to recreate the instance.
In CloudStack >= 4.9.0 it is possible to update security groups of existing instances, but as that is just added to the latest version it seems a bit too soon to start using this (causing backwards incompatibility issues for people or service providers running older versions).
* Add and update documentation
* Add acceptance tests
