Attempt to un-break Appveyor:
Attempt to un-break Appveyor:

- Put '_testing' on PYTHONPATH only for Py3k (debug grpico-on-Py3k issues
  later).

- Use 'setup.py develop' rather than 'setup.py build' to get dependencies
  installed.

- Run 'pip list' afterwards to show what got installed.

Toward #1863.

dhermes/gcloud-python,dhermes/gcloud-python,googleapis/google-cloud-python,daspecster/google-cloud-python,quom/google-cloud-python,tswast/google-cloud-python,calpeyser/google-cloud-python,GoogleCloudPlatform/gcloud-python,jonparrott/google-cloud-python,tseaver/gcloud-python,daspecster/google-cloud-python,tseaver/google-cloud-python,tseaver/google-cloud-python,tseaver/google-cloud-python,tseaver/gcloud-python,jonparrott/gcloud-python,tswast/google-cloud-python,dhermes/google-cloud-python,jgeewax/gcloud-python,elibixby/gcloud-python,calpeyser/google-cloud-python,tartavull/google-cloud-python,waprin/gcloud-python,quom/google-cloud-python,waprin/google-cloud-python,waprin/google-cloud-python,googleapis/google-cloud-python,jonparrott/gcloud-python,jonparrott/google-cloud-python,GoogleCloudPlatform/gcloud-python,tswast/google-cloud-python,Fkawala/gcloud-python,dhermes/google-cloud-python,elibixby/gcloud-python,waprin/gcloud-python,Fkawala/gcloud-python,dhermes/google-cloud-python,jgeewax/gcloud-python,tartavull/google-cloud-python