Add pillow dependency libjpeg-dev to bindep

 This should fix the error we're seeing in gate jobs:
 ValueError: jpeg is required unless explicitly disabled
 using --disable-jpeg, aborting

Change-Id: I686b21e452aad2dfb9358360137070f58dde3882
diff --git a/bindep.txt b/bindep.txt
index 1ade655..1f08a58 100644
--- a/bindep.txt
+++ b/bindep.txt
@@ -2,3 +2,4 @@
 mysql-server [test]
 postgresql [test]
 postgresql-client [test]
+libjpeg-dev [test]