remove imvirt dependency and fix openvz check

imvirt doesn't work properly on openvz anymore so the script tries to run the entropy daemon anyways. I fixed the check to look for /proc/user_beancounters instead which only exists on openvz (to my knowledge). If it exists then it skips the parts relating to rngd only. It will still generate a key however. Before you blocked out the entire segment on openvz.

shinji257@0a34812#oab-java

Tested on OpenVZ and Xen PV.

Edit: Closed #70 since I have the pull request here.