Setting custom PID file parameters.

Modified SOURCES/sysconfig-graylog2-web-interface to include the variable GRAYLOG2_PID,
setting the value to /var/run/graylog2/web-interface.pid

Adding the command linie option "-Dpidfile.path=${GRAYLOG2_PID}" to the start command
in SOURCES/init.d-graylog2-web-interface

Setting the GRAYLOG2_PID variable to /var/run/graylog2/server.pid in SOURCES/sysconfig-graylog2-server

In the start command in SOURCES/init.d-graylog2-server breaking the command line options
into individual lines to add readability to the script.

Creating the /var/run/graylog2/ directory in SPECS/graylog2-server.spec and SPECS/graylog2-web-interface.spec