Ensure only python3 is installed with bindep.txt

We no longer support python2.7 for zuul, we can be more specific
and now only install python3 libraries.

Change-Id: Ic31221cb55a09d9568a9f5f26c412c0559555f01
Signed-off-by: Paul Belanger <pabelanger@redhat.com>
diff --git a/bindep.txt b/bindep.txt
index 3dcc3e7..11ebdf5 100644
--- a/bindep.txt
+++ b/bindep.txt
@@ -13,7 +13,7 @@
 openssl-devel [platform:rpm]
 libffi-dev [platform:dpkg]
 libffi-devel [platform:rpm]
-python-dev [platform:dpkg]
-python-devel [platform:rpm]
+python3-dev [platform:dpkg]
+python3-devel [platform:rpm]
 bubblewrap [platform:rpm]
 redhat-rpm-config [platform:rpm]