Add python dev dependency

pysendfile 2.0 needs this to build

Change-Id: I40a2c08bfc6d533bdcb052d0c36353e95e059e03
diff --git a/files/apts/glance b/files/apts/glance
index 42d9fb8..9612267 100644
--- a/files/apts/glance
+++ b/files/apts/glance
@@ -1,4 +1,5 @@
 gcc
+python-dev
 python-eventlet
 python-routes
 python-greenlet