Prevent Python from importing the host's pip packages

This patch prevents Python from searching the user's installed pip
packages as well as the host's `site` package. The host's `site`
package normally performs the setup necessary to allow importing
globally installed pip packages. We don't want that.

From the upstream documentation:
https://docs.python.org/3/using/cmdline.html

    -s
        Don’t add the user site-packages directory to sys.path.
        See also PEP 370 – Per user site-packages directory

    -S
        Disable the import of the module site and the
        site-dependent manipulations of sys.path that it
        entails. Also disable these manipulations if site is
        explicitly imported later (call site.main() if you
        want them to be triggered).

Change-Id: I11a64c33920fc174dd8ac5d200e2e8550a3c084a
Signed-off-by: Philipp Schrader <philipp.schrader@gmail.com>
diff --git a/debian/opencv_python.BUILD b/debian/opencv_python.BUILD
index 5afa180..5074bd3 100644
--- a/debian/opencv_python.BUILD
+++ b/debian/opencv_python.BUILD
@@ -5,6 +5,9 @@
         include = ["**/*"],
         exclude = ["**/*.py"],
     ),
+    deps = [
+        "@python_repo//:numpy",
+    ],
     imports = ["."],
     visibility = ["//visibility:public"],
 )