Revert "Simplify create_session of lttng create command"

This reverts commit 318e4c832cc9a4209dcea885ef2a66cfd16f99d2.

The create_session function was changed making the session name not
having the date and time append to it anymore. This completely broke the
default behavior of automatic session creation. Only one possible
session name was 'auto'.

Signed-off-by: David Goulet <dgoulet@efficios.com>