[nova-consoleauth] netstat stderr should be suppressed

The nova-consoleauth RA runs `netstat -punt` several times.
Even if the RA is run as root, sometimes the following error will be printed:

(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)

The error above then ends up spamming syslog with something like

lrmd[1577]: notice: res_nova_consoleauth_monitor_5000:874125:stderr [ (Not all processes could be identified, non-owned process info ]
lrmd[1577]: notice: res_nova_consoleauth_monitor_5000:874125:stderr [ will not be shown, you would have to be root to see it all.) ]

In some cases, sockets are not associated with PIDs, therefore netstat won't be able to populate the relative column, even if run as root; see for example: https://unix.stackexchange.com/questions/97752/how-to-identify-a-process-which-has-no-pid#97753

Given that the RA is only looking at stdout anyway, I suggest for stderr to be devnull-ed.