allow creating user with no password

[CzechJiri]

function create_user exits when no password is supplied, in some cases it might be useful to create user with random long password e.g. when PG_TRUST_LOCALNET is enabled

random password can be generated for example using openssl random function

DB_PASS=$(openssl rand -base64 32)

[LongLiveCHIEF]

You can do this in your Dockerfile, example:

FROM sameersbn/postgresql

RUN bash -l -c 'echo export PG_PASSWORD="$(openssl rand -base64 32)" >> /etc/bash.bashrc'

Or via your docker run command:

docker run ---env PG_PASSWORD="$(openssl rand -base64 32)" .......