Fix database setup in admin center

Using a 7.4 snapshot from sept 24

• Setup a postgresql 9.3 database and configure it as described in the doc
• Start the nuxeo platform
• Go to admin center, change database from H2 to postgresql
• Fill the form
• Press check db parameters => parameters are OK
• Save => An error appears saying the db parameters are incorrect

This error does not happen if the nuxeo.conf file is edited to put the common and postgresql templates instead of default + setting up the db information directly into it.