Import the database as the `git` user

This ensures that all tables created during the import belong to `git`.
If you import as a different user, such as the `postgres` superuser, you
may encounter issues where the GitLab database user cannot access tables
in gitlabhq_production, _even if_ `git` is the owner of
gitlabhq_production at the time of import.

doc/update/mysql_to_postgresql.md

@@ -19,7 +19,9 @@ git clone https://github.com/lanyrd/mysql-postgresql-converter.git
 cd mysql-postgresql-converter
 mysqldump --compatible=postgresql --default-character-set=utf8 -r databasename.mysql -u root gitlabhq_production
 python db_converter.py databasename.mysql databasename.psql
-psql -f databasename.psql -d gitlabhq_production
+
+# Import the database dump as the application database user
+sudo -u git psql -f databasename.psql -d gitlabhq_production
 
 sudo service gitlab start
 ```