Allow openebs provisioner to identify namespace
Allow openebs provisioner to identify namespace

OpenEBS provisioner should identify its own namespace and
search for `maya-apiserver-service` in the same namespace.
Here, we are reading the namespace of openebs-provisioner
from `OPENEBS_NAMESPACE` env variable. If provisioner is
unable to find `OPENEBS_NAMESPACE` variable then it should
set namespace to default.

To set OPENEBS_NAMESPACE to namespace.
In openebs-operator.yaml add following:

```
env:
- name: OPENEBS_NAMESPACE
          valueFrom:
            fieldRef:
              fieldPath: metadata.namespace

```

fixes: https://github.com/openebs/openebs/issues/306
fixes: https://github.com/kubernetes-incubator/external-storage/issues/424

humblec/external-storage,humblec/external-storage,humblec/external-storage,kubernetes-incubator/external-storage,kubernetes-incubator/external-storage,kubernetes-incubator/external-storage