casper fails on generating SSL and anything that uses /dev/urandom

[Arthur Lutz (Logilab)]

First thing that fails is :

Begin: Regenerating SSL certificate... ... Could not create certificate. Openssl output was:
unable to load 'random state'
This means that the random number generator has not been seeded

Then :

OSError: [Errno 2] No such file or directory: '/dev/urandom'

Full trace of casper.log here : http://paste.ubuntu.com/1447308/

casper.conf is ::

export USERNAME="custom"
export USERFULLNAME="Live session user"
export HOST="custom"
export BUILD_SYSTEM="Ubuntu"
export FLAVOUR="custom"

Using precise pangolin 12.04 with casper version 1.315

In the past I had some success hacking around this problem by using

+export UNIONFS="unionfs-fuse"

or

+export UNIONFS="aufs"

That doesn't seem to work anymore.