ipc: VCSecurityLevel->Security and no longer a stream opt.

SecurityLevel is not handled only in server.go and client.go.
Everywhere else in the ipc stack, nil principal means SecurityNone.

This also fixes https://github.com/veyron/release-issues/issues/1423
in the process.

MultiPart: 1/2
Change-Id: I55646e574e43b633c69300b1fecb623c95340bbc
20 files changed