Update dr debian dependencies

[convolu]

From recent attempts to deploy, I think that the debian dependencies listed in the wiki are not correct (at least in jessie). I think that the following work:

git
devscripts
tar
gzip
debhelper
debootstrap
qemu-user-static
schroot
rubygems
build-essential
curl
reprepro
rng-tools
dpkg-sig

[mcdope]

ruby-dev is missing, but yeah - that list works if i add that.