Fix: rotation_unavailable returned on failure to read time

Fix: rotation_unavailable returned on failure to read time

A "rotation feature unavailable" error code is returned if the
session daemon fails to sample time. The TIME(2) man page has
makes no mention of an error that could happen in this use case
(as time()'s parameter is NULL, EFAULT does not apply).

However, a more general error code is more appropriate should
this call fail.

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