Fixes#7543 where creating a CloudWatch Group, then deleting it from the
console will cause no action on refresh / plan
```
% make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSCloudWatchLogGroup_'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
TF_ACC=1 go test ./builtin/providers/aws -v
-run=TestAccAWSCloudWatchLogGroup_ -timeout 120m
=== RUN TestAccAWSCloudWatchLogGroup_importBasic
--- PASS: TestAccAWSCloudWatchLogGroup_importBasic (18.10s)
=== RUN TestAccAWSCloudWatchLogGroup_basic
--- PASS: TestAccAWSCloudWatchLogGroup_basic (17.34s)
=== RUN TestAccAWSCloudWatchLogGroup_retentionPolicy
--- PASS: TestAccAWSCloudWatchLogGroup_retentionPolicy (49.81s)
=== RUN TestAccAWSCloudWatchLogGroup_multiple
--- PASS: TestAccAWSCloudWatchLogGroup_multiple (23.74s)
=== RUN TestAccAWSCloudWatchLogGroup_disappears
--- PASS: TestAccAWSCloudWatchLogGroup_disappears (15.78s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 124.789s
```