Sanitize input before creating IPC socket.

Sockets are created by the zeromq driver
for the topic specified by each incoming message.

Because the topic is arbitrarily supplied by the sender,
path separators in the topic must be illegal.

Fixes bug 1122763

Change-Id: Iccdb9b69e646bfe7665ee34c367fd4019db25f17
Merge "Sanitize input before creating IPC socket."