add dduvall to researchers group

follow-up to Ia41aae4d20686 and Ia6a943b03c104

the group "statistics-users" is not sufficient,
because it does not give access to the researchdb
password

though not specifically requested, this was the intention
in RT: 8394 , otherwise we give him shell, and mysql
just not the db password

Change-Id: I0226fe266c0c1950bf9996154ce4e7063d42bb71
RT: 8394
RT: 7105