fix #7868: user management: privileges: fix Sys.PowerMgmt description

The description was taken over from VM.PowerMgmt, but nodes cannot be
started, stopped or reset via the API. The privilege is only required
for rebooting and shutting down a node, and for waking up a node via
Wake-on-LAN.

Signed-off-by: Michal Fox <me@dualfroz.com>

pveum.adoc

@@ -893,7 +893,7 @@ Node / System related privileges::
 * `Sys.Console`: console access to node
 * `Sys.Incoming`: allow incoming data streams from other clusters (experimental)
 * `Sys.Modify`: create/modify/remove node network parameters
-* `Sys.PowerMgmt`: node power management (start, stop, reset, shutdown, ...)
+* `Sys.PowerMgmt`: node power management (reboot, shutdown, Wake-on-LAN)
 * `Sys.Syslog`: view syslog
 * `User.Modify`: create/modify/remove user access and details.