Ram usage as unknown when LXC is OFF

[snp88]

Hi
First at all your integration is great :)

i have small request :)

Can we show Ram usage as 0% instead of unknown value when the LXC is off

0 is not far from true right :) when the lxc is off it don't use any RAM.
I think 0 value is more elegant
Let me know what you think

[dougiteixeira]

Added in #306. It will be available in the next version (3.4.2).