sysutils/graylog: enable using alternate JVM versions

Future graylog versions in the 5.x series require both newer
java versions, and migration from ElasticSearch to OpenSearch.

This patch helps smooth the migration path.

Reported by:	Einar Bjarni Halldórsson <einar@isnic.is>

sysutils/graylog/Makefile

@@ -1,5 +1,6 @@
 PORTNAME=	graylog
 DISTVERSION=	4.3.9
+PORTREVISION=	1
 CATEGORIES=	sysutils java
 MASTER_SITES=	https://downloads.graylog.org/releases/
 DISTFILES=	graylog/${DISTNAME}${EXTRACT_SUFX} \
@@ -18,7 +19,7 @@ LICENSE_PERMS_SSPLv1=	dist-mirror dist-sell pkg-mirror pkg-sell auto-accept
 USES=		cpe tar:tgz
 USE_JAVA=	yes
 
-JAVA_VERSION=	1.8+
+JAVA_VERSION=	8+
 JAVA_EXTRACT=	yes
 JAVA_RUN=	yes
 
@@ -38,7 +39,8 @@ GRAYLOG_LOGS_DIR=	/var/log/graylog
 SUB_LIST=	GRAYLOG_DATA_DIR=${GRAYLOG_DATA_DIR} \
 		GRAYLOG_LOGS_DIR=${GRAYLOG_LOGS_DIR} \
 		GRAYLOGGROUP=${GRAYLOGGROUP} \
-		GRAYLOGUSER=${GRAYLOGUSER}
+		GRAYLOGUSER=${GRAYLOGUSER} \
+		JAVA_HOME=${JAVA_HOME}
 
 PLIST_SUB=	DISTVERSION=${DISTVERSION} \
 		GRAYLOG_DATA_DIR=${GRAYLOG_DATA_DIR} \

sysutils/graylog/files/graylog.in

@@ -45,6 +45,10 @@
 # graylog_log_config (string):
 #   Default value: %%ETCDIR%%/server/log4j2.xml
 #   Path to the Graylog Server logfile
+#
+# graylog_java_home (path):
+#   Default value: %%JAVA_HOME%%
+#   Set it to the root of the JDK to use.
 
 . /etc/rc.subr
 
@@ -63,6 +67,7 @@ load_rc_config $name
 : ${graylog_logs_dir:="%%GRAYLOG_LOGS_DIR%%"}
 : ${graylog_run_dir:="/var/run/graylog"}
 : ${graylog_log_config:="%%ETCDIR%%/log4j2.xml"}
+: ${graylog_java_home:="%%JAVA_HOME%%"}
 
 java_options=" \
     -Djava.awt.headless=true \
@@ -103,6 +108,8 @@ command_args=" \
     --no-pid-file \
     --configfile ${graylog_config}"
 
+export JAVA_HOME=${graylog_java_home}
+
 required_files="%%LOCALBASE%%/bin/java ${graylog_config}"
 
 graylog_precmd() {