removed nginx killing

* nginx is not killed anymore
* if a user is upgrading from a playbook version without supervisor (before commit cc31c0776) or running other nginx instances:
  uncomment last task in roles/redmine/nginx.yml and kill nginx manually when it pauses
don't remove testing gems from redmine Gemfile

* conflicts with plugins seem to be resolved now => not needed anymore
fixed problem with empty OCSP certificate chain name...
commented out nginx pause

* not needed for fresh installations and poses problems with inabox