Make log file dir configurable.

src/deb/init/mon-thresh.conf

@@ -6,6 +6,12 @@ start on runlevel [2345]
 console log
 respawn
 
+pre-start script
+if [ -r /etc/default/mon-thresh ]; then
+        . /etc/default/mon-thresh
+fi
+end script
+
 setgid thresh
 setuid thresh
 exec /usr/bin/java -Xmx8g -cp /opt/mon/mon-thresh.jar com.hpcloud.mon.ThresholdingEngine /etc/mon/mon-thresh-config.yml topology-name

src/main/resources/logback.xml

@@ -9,7 +9,7 @@
     </appender>
 
     <appender name="FILE" class="ch.qos.logback.core.FileAppender">
-        <file>mon-thresh.log</file>
+        <file>${LOGDIR}/mon-thresh.log</file>
 
         <encoder>
             <pattern>%date %level [%thread] %logger{10} [%file:%line] %msg%n</pattern>