* refactoring existing cluster / firewall API for better composition
* add basic security groups API
fix linter errors
* add rules API
* fix after renaming resourceVirtualEnvironmentClusterIPSet
* fix linter errors
* make linter happy
* even more refactoring
* tidy up datasources
* in refactoring spree
* update examples
* fix firewall resource/datasource & client error handling
* add ipset(s) datasource
* update docs
* add security group resource with rules
* docs
* fix security group update, TODO: rule update
* fix after rebase
* add rule update, extract common rule schema, refactor group
* fix linter errors
* bump linter for ci
* make alias and ipset reusable
* make security group reusable
* refactor datasources
* add security group datasources
* fix linter errors
* update docs
TODO: documentation for group datasources
* add sg docs, update doc index
* minor cleanup
* fix examples & tests
* stub for firewall-level options and rules
* extract firewall interface
* add firewall options and rules on the cluster level
TODO: issues with rule list management
* refactor all resources format AGAIN, now more flat, without complex subresources
* sort out hierarchy of APIs and remove duplication in API wrappers
* bring back security group
* finally, working rules
* restore cluster firewall option
* add containers support
* add options
* move rules back under security group, update docs
* fix vm_id / container_id attrs
* add examples
* cleanup
* more cleanup
Release-As: 0.17.0-rc1
