Test fix: LTTNG_SESSION_CONFIG_XSD_PATH expects an absolute path

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Fix: "Any" loglevel's value is -1 and not 0

lttng_disable_event_ext() was erroring-out on loglevel != 0.
loglevel 0 is a valid level whereas "-1" is used an unknown/unspecified
in the rest of the code.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Fix: Don't leave events enabled if they were saved in a disabled state

Events are enabled by default on creation. The session configuration
loader must make sure to disable them after creation when restoring an
event that was saved in the "disabled" state.

Reported-by: Marcel Hamer <marcel.hamer@ericsson.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Tests: Add a test to check disabled events are loaded in the correct state

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