Description of problem:
After oc import-image with non-existent tag, it outputs inconsistent messages for imagestreams with and without spec.dockerImageRepository.

Version-Release number of selected component (if applicable):
oc v1.3.0-alpha.1-439-g604ae17
kubernetes v1.3.0-alpha.3-599-g2746284

How reproducible:
Always

Steps to Reproduce:
1. Create a new ImageStream
$ cat python.json
{
    "kind": "ImageStream",
    "apiVersion": "v1",
    "metadata": {
      "name": "python",
      "creationTimestamp": null
    },
    "spec": {
      "dockerImageRepository": "wsun/python-33-centos"
      }
}

$ oc create -f python.json

2. Import image with a non-existent tag:
$ oc import-image python:notexist
The import completed successfully.
...

Tag		Spec				Created		PullSpec					Image
latest		wsun/python-33-centos:latest	29 minutes ago	wsun/python-33-centos@sha256:354d212f9a8c77...	<same>
...
notexist	wsun/python-33-centos		1 seconds ago	wsun/python-33-centos@sha256:354d212f9a8c77...	<same>

3 $ oc edit is python # Under 'spec', remove dockerImageRepository: wsun/python-33-centos
imagestream "python" edited

4 Try import-image with non-existent tag again:
$ oc import-image python:none
error: the tag "none" does not exist on the image stream - choose an existing tag to import or use the 'tag' command to create a new tag

Actual results:
For a non-existent tag, step 2 succeeds and step 4 shows error.

Expected results:
For a non-existent tag, step 2 should also output message to notify that the given tag is not existent.

Additional info: