Fixed parameter order in test

Params were around the wrong way. Test was passing coincidentally.
Issue #1843: replace correct ACL association

Fixes problem where an ACL is associated with multiple subnets, and
associate_network_acl replaces a random other subnet's association
to the ACL.
Merge pull request #1844 from drrb/issue-1843

Replace correct VPC ACL association instead of just the first one. Fixes #1844, #1843.