Small change to the test as it was failing sometimes as it was using the
same identifier. The small change has made it more stable when running
it in quick succession as it isn't an update
```
make testacc TEST=./builtin/providers/aws
TESTARGS='-run=TestAccAWSIAMGroup_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSIAMGroup_
-timeout 120m
=== RUN TestAccAWSIAMGroup_importBasic
--- PASS: TestAccAWSIAMGroup_importBasic (14.14s)
=== RUN TestAccAWSIAMGroup_basic
--- PASS: TestAccAWSIAMGroup_basic (22.88s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 37.040s
```
