When creating a new node, OpenStack and AWS use different names for ex argument for security groups although the underlying feature is the same.
OpenStack uses 'ex_security_groups'
AWS uses 'ex_securitygroup'
Proposed solution: rename AWS argument to match OpenStack's. (as both support multiple groups)
If this is problem because it is not backwards compatible, maybe adding alias 'ex_security_groups' to AWS makes sense.