Install cryptsetup on the n-cpu nodes

test_encrypted_cinder_volumes.* tempest test failes,
when cryptsetup package is not installed.

The following error can be seen in the n-cpu log:
Stderr: u'/usr/bin/nova-rootwrap: Executable not found: cryptsetup
(filter match = cryptsetup)\n'

Change-Id: I86603f1301fa946c8bb22de3e69a2ec1ab7f1ef3
diff --git a/files/rpms/n-cpu b/files/rpms/n-cpu
index c1a8e8f..81278b3 100644
--- a/files/rpms/n-cpu
+++ b/files/rpms/n-cpu
@@ -4,4 +4,4 @@
 genisoimage
 sysfsutils
 sg3_utils
-
+cryptsetup