fs-sink: handle trace name

fs-sink: handle trace name

Now the fs-sink uses the trace name to create the output path.
The trace name is appended after the path argument passed on the command
line.
If the resulting path exists, the plugin increments a numerical suffix
until it finds one or reaches INT_MAX.

The trace name is refused if it is ".." or contains "../".

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