add support for ubuntu 14.04

Ubuntu 14.04 includes postgresql 9.3, and no longer symlinks the ssl
certificates into the postgresql data directory, so we need to set the
certificates to the snakeoil certs in /etc

I"ve tested this and it works in Ubuntu Server 14.04, and I checked that 13.10 is the cut off point for 9.1, so 14.04 must be the first version that uses 9.3.