database backup trying to use AWS secrets rather than IAM when accesskey and secretkey are blank

I have IAM setup and have confirmed it works in the deis namespace by running up generic ubuntu and accessing the bucket successfully. However the database log is showing this:

```
Performing an initial backup...
wal_e.main INFO MSG: starting WAL-E
DETAIL: The subcommand is "backup-push".
STRUCTURED: time=2017-04-13T21:05:13.346499-00 pid=111
wal_e.main ERROR MSG: AWS Access Key credential is required but not provided
HINT: Pass "--aws-access-key-id" or set the environment variable "AWS_ACCESS_KEY_ID".
STRUCTURED: time=2017-04-13T21:05:13.346858-00 pid=111
```

My values config snippets are:

```
global:
# Set the storage backend
#
# Valid values are:
# - s3: Store persistent data in AWS S3 (configure in S3 section)
# - azure: Store persistent data in Azure's object storage
# - gcs: Store persistent data in Google Cloud Storage
# - minio: Store persistent data on in-cluster Minio server
storage: s3
.
.
.
database_location: "on-cluster"
.
.
.
s3:
# Your AWS access key. Leave it empty if you want to use IAM credentials.
accesskey: ""
# Your AWS secret key. Leave it empty if you want to use IAM credentials.
secretkey: ""
# Any S3 region
region: "us-west-2"
# Your buckets.
registry_bucket: "tectonic-deis-registry"
database_bucket: "tectonic-deis-database"
builder_bucket: "tectonic-deis-builder"
```

This is with chart 2.13 (assuming this is the latest).