Fixes#6758
We used to throw an error when this was the case - we should refresh
from state so the association can be recreated
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSEIPAssociation_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2016/09/26 16:42:37 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSEIPAssociation_ -timeout 120m
=== RUN TestAccAWSEIPAssociation_basic
--- PASS: TestAccAWSEIPAssociation_basic (272.92s)
=== RUN TestAccAWSEIPAssociation_disappears
--- PASS: TestAccAWSEIPAssociation_disappears (119.62s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws392.559s
```
* New top level AWS resource aws_eip_association
* Add documentation for aws_eip_association
* Add tests for aws_eip_association
* provider/aws: Change `aws_elastic_ip_association` to have computed
parameters
The AWS API was send ing more parameters than we had set. Therefore,
Terraform was showing constant changes when plans were being formed
Clint