Enable md5 on Postgresql for RHEL

[espenfl]

Right now we use trust policy for Postgresql on RHEL. Change this to md5.

[ltalirz]

One step in this direction can be to only allow passwordless connection for the postgres user, and only via unix domain socket.

I.e.

• change all trust to md5
• add line local all postgres trust

This means psql -U postgres will still work for any user; pgsu should be able to detect this (? to check)

P.S. Just to be clear: the current settings allow passwordless access to any database user, but only from the host VM.
Access to the postgres server from other hosts is disallowed.