Add infrastructure to download deb packages for the build

See //debian/packages.bzl for a bit more detail.

In this patch I've added the Python packages that we'll use later on
in the sandbox setup.

Change-Id: Ia651d778cc85ecdbf78d50230fea652f7633f799
diff --git a/WORKSPACE b/WORKSPACE
index e1cb1f8..1dc4a36 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -1,5 +1,10 @@
 workspace(name = 'org_frc971')
 
+load("//debian:python.bzl", python_debs="files")
+load("//debian:packages.bzl", "generate_repositories_for_debs")
+
+generate_repositories_for_debs(python_debs)
+
 new_local_repository(
   name = 'usr_repo',
   path = '/usr',