services: fix common problems in prereqs
  - home directory parent doesn't exist
  - incorrect invocation of su
  - unneeded invocation of su
  - other minor stuff
pkg/dovecot: disable bzlib
pkg/dpkg: disable building all non-essential tools
pkg/postgresql: add readline dependency
pkg/tor: update version
write-hd-image-squash: fix su setuid, both in image creation and on rootfs
  * use pseudo definition for bin/su's mode
  * do not use /tmp for creating images as that has restrictions to setuid
install-service: use --force from packages
haveged: force service install, svc exit on prereqs