Open Terminal

test@example:~$ sudo su postgres
[sudo] password for test: 
postgres@example:/home/test$ psql
psql (9.5.10)
Type "help" for help.
postgres=# \l

Thanks !

iWesabe 

enter psql -l from terminal

Login as postgres user in terminal:

sudo su postgres

... and then

psql -l

for list all databases

You can all you databases (not only those ones that are OpenERP ones) by running this SQL request : "SELECT datname FROM pg_catalog.pg_database"