Changes

Updating docker --build-arg test due to docker code change
Docker changed the error for a non-existent --build-arg to a warning and
changed the text of the message slightly, breaking one of our tests. 
Docker change:
https://github.com/moby/moby/commit/f150f42009dddb4f9b8d4ceef8763af701b0d0f9
Fixes: #16197
 (commit: 7c3edb3)

cleanup imagestreamtag desc
 (commit: e20d454)