Dont use DNS style addressing for GetBucketLocation

This fixes an issue when you try to get bucket location
for a bucket in eu-central-1.  You now do not need a region
specified.

For example, you previously needed:

```
$ aws s3api get-bucket-location --bucket jamesls-eu-central-1 --region eu-central-1
{
    "LocationConstraint": "eu-central-1"
}
```

which defeated the purpose of get-bucket-location.  Now the region doesn't matter:

```
$ aws s3api get-bucket-location --bucket jamesls-eu-central-1 --region us-east-1
{
    "LocationConstraint": "eu-central-1"
}
$ aws s3api get-bucket-location --bucket jamesls-eu-central-1 --region us-west-2
{
    "LocationConstraint": "eu-central-1"
}
$ aws s3api get-bucket-location --bucket jamesls-eu-central-1 --region ap-northeast-1
{
    "LocationConstraint": "eu-central-1"
}
```


cc @kyleknap @danielgtaylor 
It's not obvious from this test, but self.endpoint is actually the endpoint for us-east-1, defined in the base classes's setUp.