Install systemd python bindings by default

These are needed for oslo.log to use journald support. They are
*probably* already installed, but just in case we force install them.

Change-Id: I0dc66bd2628ff4b3e1caa7ab4366d7f36ff7ea94
diff --git a/files/debs/general b/files/debs/general
index c121770..3a0e241 100644
--- a/files/debs/general
+++ b/files/debs/general
@@ -25,6 +25,7 @@
 python2.7
 python-dev
 python-gdbm # needed for testr
+python-systemd
 screen
 tar
 tcpdump