Honor JAVA_HOME in graalpy.sh

(cherry picked from commit 10dc0d8)

Author: steve-s

graalpython/lib-graalpython/modules/standalone/app/graalpy.sh

@@ -12,10 +12,16 @@ while [ -h "$source" ] ; do
 done
 location="$( cd -P "$( dirname "$source" )" && pwd )"
 
+if [ -z "$JAVA_HOME" ]; then
+    JAVA=$JAVA_HOME/bin/java
+else
+    JAVA=java
+fi
+
 for var in "$@"; do    
     args="${args}$(printf "\v")${var}"
 done
 
 export GRAAL_PYTHON_ARGS=$args
-echo graalpy.sh is going to execute: mvn -f "${location}/pom.xml" exec:exec -Dexec.executable=java -Dexec.args="--module-path %classpath '-Dorg.graalvm.launcher.executablename=$0' --module org.graalvm.py.launcher/com.oracle.graal.python.shell.GraalPythonMain"
-mvn -f "${location}/pom.xml" exec:exec -Dexec.executable=java -Dexec.args="--module-path %classpath '-Dorg.graalvm.launcher.executablename=$0' --module org.graalvm.py.launcher/com.oracle.graal.python.shell.GraalPythonMain"
+echo graalpy.sh is going to execute: mvn -f "${location}/pom.xml" exec:exec -Dexec.executable=$JAVA -Dexec.args="--module-path %classpath '-Dorg.graalvm.launcher.executablename=$0' --module org.graalvm.py.launcher/com.oracle.graal.python.shell.GraalPythonMain"
+mvn -f "${location}/pom.xml" exec:exec -Dexec.executable="${JAVA}" -Dexec.args="--module-path %classpath '-Dorg.graalvm.launcher.executablename=$0' --module org.graalvm.py.launcher/com.oracle.graal.python.shell.GraalPythonMain"