testr requires python's gdbm

Debian/Ubuntu have *helpfully* removed gdbm from the base python
package and put it into another package, which is not dragged in by
installing python. Testr doesn't function without this.

We should ensure this always gets installed.

Depends-On: If48a8444b02ee1e105bc1d9ce78a0489ea0c405b

Change-Id: I85a0ffe5ee384e055e78fd3164c27d42a86bc39d
diff --git a/files/debs/general b/files/debs/general
index c27b77d..1460526 100644
--- a/files/debs/general
+++ b/files/debs/general
@@ -17,6 +17,7 @@
 tar
 python-dev
 python2.7
+python-gdbm # needed for testr
 bc
 libyaml-dev
 libffi-dev