Adding rundamentary configtest function

https://github.com/corey-hammerton/graylog2-rpms/issues/5

Files Modified:
SOURCES/init.d-graylog2-server

Adding a configtest function to SOURCES/init.d-graylog2-server
to test the syntax of the configuration file.

Right now this is just a simple function. I would like to validate
the log4j configuration but in order to do that will have to
implement said configuration differently.
Merge branch 'master' into configtest
Testing the log4j configuration file with xmllint

https://github.com/corey-hammerton/graylog2-rpms/issues/5

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

Creating new variable GRAYLOG2_LOG_CONF in
SOURCES/sysconfig-graylog2-server in replacement for the
fixed string in the ADDITIONAL_JAVA_OPTS variable. This is the
only possible way to test the syntax of the log4j configuration.
Doing the same in SOURCES/init.d-graylog2-server

Checking for the existence of the GRAYLOG2_LOG_CONF variable in
SOURCES/init.d-graylog2-server before running xmllint on it in the
configtest function.

Adding a new RPM dependency in SPECS/graylog2-server.spec for
libxml2, the provider of /usr/bin/xmllint.
Adding a configtest function in the web-interface init-script.

https://github.com/corey-hammerton/graylog2-rpms/issues/5

Files Modified:
SOURCES/init.d-graylog2-web-interface
SOURCES/sysconfig-graylog2-web-interface
SPECS/graylog2-web-interface.spec

Adding a new variable GRAYLOG2_LOG_CONF in
SOURCES/init.d-graylog2-web-interface and
SOURCES/sysconfig-graylog2-web-interface which eliminates the need
to hard-code the settings in the ADDITIONAL_JAVA_OPTS variable.
This is the only possible way to test the syntax of the log4j.xml
configuration.

Adding the configtest function to SOURCES/init.d-graylog2-web-interface
which only runs xmllint on the GRAYLOG2_LOG_CONF file if it
exists. Since the web-interface doesn't have configtest
functionality we cannot check the functionality of the web-interface
configuration.

Adding a dependency for libxml2 in SPECS/graylog2-web-interface.spec.
In order to be able to run xmllint.
Adding configtest functionality to the radio package.

https://github.com/corey-hammerton/graylog2-rpms/issues/5

Files Modified:
SOURCES/init.d-graylog2-radio
SOURCES/sysconfig-graylog2-radio
SPECS/graylog2-radio.spec

The same functionality for these files have been duplicated and
adapted from the web-interface package (see this commit's parent).