Silence cache warning for dom0.
Silence cache warning for dom0.

At the moment the log file is accumulating a line every five seconds,
I can't see this message is useful.

Signed-off-by: Simon Rowe <e4b8acc9a3d4f7423a8172304282dedbc4041c17@eu.citrix.com>

johnelse/rrdd-plugins,koushikcgit/rrdd-plugins,martinjorge/rrdd-plugins,koushikcgit/rrdd-plugins,johnelse/rrdd-plugins,martinjorge/rrdd-plugins