permslip signer clutters stdout

[flihp]

This is cosmetic. The permslip signer dumps some stuff to stdout that we should ignore. Instead it ends up cluttering output from the manufacture command:

$ dice-mfg manufacture --require-release-policy false permslip
sending ping ... success
setting platform id to: "PDV2:PPP-PPPPPPP:RRR:0000000000B" ... success
getting CSR ... success
checking CSR ... success
Wrote to 0000000000B/ca.cert.pem
setting Intermediate cert ... success
Wrote to 0000000000B/PDV2:PPP-PPPPPPP:RRR:0000000000B.cert.pem
success
setting PlatformId cert ... success
sending Break ... success

The lines we should be ignoring are: Wrote to 0000000000B/ca.cert.pem and Wrote to 0000000000B/PDV2:PPP-PPPPPPP:RRR:0000000000B.cert.pem. Looks like there's an extra success message too?