The rb_sysopen runs as www-data that needs to access to production.log,
backend_access.log and database.yml.

Revert the group owner to www-data to avoid following errors:

 Rails Error: Unable to access log file. Please ensure that
 /usr/share/obs/api/log/production.log exists and is writable (ie, make
 it writable for user and group: chmod 0664
 /usr/share/obs/api/log/production.log). The log level has been raised
 to WARN and the output directed to STDERR until the problem is fixed.
 rake aborted!
 Errno::EACCES: Cannot load `Rails.application.database_configuration`:
 Permission denied @ rb_sysopen - /usr/share/obs/api/config/database.yml
 /usr/share/obs/api/config/environment.rb:30:in `<top (required)>'
 Errno::EACCES: Permission denied @ rb_sysopen -
 /usr/share/obs/api/config/database.yml
 /usr/share/obs/api/config/environment.rb:30:in `<top (required)>'
 Tasks: TOP => environment
 (See full trace by running task with --trace)
 Errno::EACCES: Permission denied @ rb_sysopen -
 /usr/share/obs/api/log/backend_access.log
 /usr/share/obs/api/lib/opensuse/backend.rb:14:in `new'
 /usr/share/obs/api/lib/opensuse/backend.rb:14:in `<class:Backend>'
 /usr/share/obs/api/lib/opensuse/backend.rb:6:in `<module:Suse>'
 /usr/share/obs/api/lib/opensuse/backend.rb:5:in `<top (required)>'
 /usr/share/obs/api/app/models/project.rb:1:in `<top (required)>'
 /usr/share/obs/api/app/indices/project_index.rb:2:in `block in <top
 (required)>'
 Tasks: TOP => ts:index
 (See full trace by running task with --trace)

Signed-off-by: Andrew Lee (李健秋) <ajqlee@debian.org>