Isolate tests with external server dependencies

Several tests at several layers (unit, integration, test-cmd.sh, etc) have dependencies on external servers like dockerhub, etc. When these servers have issues, they can block the merge queue.

Possible failures (all from https://github.com/openshift/origin/pull/3619):

--- FAIL: TestImage (0.91s)
    client_test.go:105: unexpected error: error getting X-Docker-Token from openshift/origin-not-found: Get http://index.docker.io/v1/repositories/openshift/origin-not-found/images/: EOF

error: no image or template matched "mysql"
!!! Error in hack/test-cmd.sh:501
  '[ "$(oc new-app mysql --name=db | grep db)" ]' exited with status 1
Call stack:
  1: hack/test-cmd.sh:501 main(...)
Exiting with status 1

--- FAIL: TestRunAll (2.03s)
    newapp_test.go:686: emptyDir volumes: Error mismatch! Expected <nil>, got no image or template matched "mysql": the image "ee2cb077006e3385648619d6adf66d5ac53cfb11c4b2708636c5be0a12b23ff7" in repository "library/mysql" was not found and may have been deleted

Our core tests should be able to run with minimal dependencies on external servers. Tests that depend on other servers should be moved to an extended test suite.

Start by examining client_test.go, hack/test-cmd.sh around line 501, and newapp_test.go around TestRunAll and line 686. Reproduce the Docker Hub and mysql failures, then identify which external-server-dependent tests belong in an extended suite while keeping core tests runnable with minimal external dependencies.