add integration tests for custom config files

test/integration/files/custom_config/jvm.options

@@ -0,0 +1,34 @@
+## JVM configuration CUSTOM FILE
+
+-Xms2g
+-Xmx2g
+-XX:+UseConcMarkSweepGC
+-XX:CMSInitiatingOccupancyFraction=75
+-XX:+UseCMSInitiatingOccupancyOnly
+-Des.networkaddress.cache.ttl=60
+-Des.networkaddress.cache.negative.ttl=10
+-XX:+AlwaysPreTouch
+-Xss1m
+-Djava.awt.headless=true
+-Dfile.encoding=UTF-8
+-Djna.nosys=true
+-XX:-OmitStackTraceInFastThrow
+-Dio.netty.noUnsafe=true
+-Dio.netty.noKeySetOptimization=true
+-Dio.netty.recycler.maxCapacityPerThread=0
+-Dlog4j.shutdownHookEnabled=false
+-Dlog4j2.disable.jmx=true
+-Djava.io.tmpdir=${ES_TMPDIR}
+-XX:+HeapDumpOnOutOfMemoryError
+-XX:HeapDumpPath=${heap.dump.path}
+-XX:ErrorFile=/var/log/elasticsearch/hs_err_pid%p.log
+8:-XX:+PrintGCDetails
+8:-XX:+PrintGCDateStamps
+8:-XX:+PrintTenuringDistribution
+8:-XX:+PrintGCApplicationStoppedTime
+8:-Xloggc:/var/log/elasticsearch/gc.log
+8:-XX:+UseGCLogFileRotation
+8:-XX:NumberOfGCLogFiles=32
+8:-XX:GCLogFileSize=64m
+9-:-Xlog:gc*,gc+age=trace,safepoint:file=/var/log/elasticsearch/gc.log:utctime,pid,tags:filecount=32,filesize=64m
+9-:-Djava.locale.providers=COMPAT