Added libffi-dev to the needed packages

Change-Id: Ida7001886f17c9413b33312f12f2478a54bd6c90
diff --git a/files/rpms/swift b/files/rpms/swift
index ee1fad8..2cc4a0b 100644
--- a/files/rpms/swift
+++ b/files/rpms/swift
@@ -1,5 +1,6 @@
 curl
 gcc
+libffi-devel
 memcached
 python-configobj
 python-coverage