Moving the server's log4j and configuration file to a new path

https://github.com/corey-hammerton/graylog2-rpms/issues/4

Files Modified:
SOURCES/sysconfig-graylog2-server
SPECS/graylog2-server.spec

- Installing source3 in SPECS/graylog2-server.spec to path
  /etc/graylog2/server/log4j.xml
- Installing the graylog2.conf.example file now in
  /etc/graylog2/server/graylog2.conf

- Updating the log4j.configuration property in
  SOURCES/sysconfig-graylog2-server with the new path
  /etc/graylog2/server/log4j.xml
- Adding the local variable GRAYLOG2_CONF to overwrite the default
  value in SOURCES/init.d-graylog2-server. Current value is
  /etc/graylog2/server/graylog2.conf