Adding a sleep command after the startup command in init.d-graylog2-server

https://github.com/corey-hammerton/graylog2-rpms/issues/1

This is all that was accomplished in script level port testing.
I tried to write a new function rest_listening to do that script level port testing, but every test
I ran always returned an exit code of 1.

At least adding a delay in the startup will prevent future errors from occurring.