MAINT CI: collect rackspace DNS info

Sometimes the following installation step fails:

    pip install -r continuous_integration/appveyor/requirements.txt

This steps download prebuilt version of numpy and scipy for windows that
are hosted on a rackspace container. In order to be able to report
the necessary debugging info to the rackspace cloud support team we need
to know the location of the failing hosts.

appveyor.yml

@@ -30,6 +30,9 @@ environment:
 
 
 install:
+  # Collect info to debug rare and random download errors from Rackspace cloud store
+  - "nslookup 28daf2247a33ed269873-7b1aad3fab3cc330e1fd9d109892382a.r6.cf2.rackcdn.com"
+
   # Install Python (from the official .msi of http://python.org) and pip when
   # not already installed.
   - "powershell ./continuous_integration/appveyor/install.ps1"