As the wait-for-it script is started before the parsing of the command
line, it is always started. It can be a problem if a user wants to start
some other binary than odoo (for example a shell).
Also, the wait-for-it script is only checking if a port is open on a
host and then waits 5 seconds before starting Odoo.
With this commit, the wait-for-it script is replaced by a more useful
custom python script that checks if the postgresql server is able to
handle a connection with the given parameters. Odoo then starts whenever
it's ready or fails after a 30 sec timeout.
