new-app creates unnecessary imagestream

[bparees]

#20052 appears to have broken new-app's behavior.

Running in an empty project:

oc new-app https://github.com/openshift/nodejs-ex

creates an imagestreamtag named "nodejs:10" in the current namespace.

The buildconfig it creates references the openshift/nodejs:10 IST as expected, but the currentnamespace/nodejs:10 IST is also created.

[bparees]

(I haven't confirmed that was the PR that broke it, but it seems suspicious anyway)

[coreydaley]

(3) Reuse existing imagestreams with new-app [app_creation][tech_debt]