Refactor/catch driver errors (#110)

* fix: adding lan to existing natgateway, setting nat ip

* refactor: always perform rollback on error, fix tests

* refactor: move methods to different file

* fix: review changes

* test: updated test to check method arguments

* test: updated more tests

* test: added more tests

* fixed tests

* test: nat patch tests, improved coverage

* test: fix tests