Send session creation time to relay daemon when supported

A recent commit changed the way the creation timestamp was added to a
session's output path; the session creation timestamp is now (2.11+)
sampled at creation time and formatted when the session's output
directory is created.

The 2.11+ version of the session and stream creation commands allow
the relay daemon to use all components of the path independently to
format an output path rather than relying on the session daemon peer
to format it ahead of time.

In order to maintain the timestamped session folder name created by
previous versions, the relay daemon now receives the session's
creation timestamp and formats it rather than relying on it being
"cooked" into the transmitted session name.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>