onos command to use Java 1.8

Change-Id: I8741c41a74dba3b816a838aa1db1588be7f9816a

@@ -3,7 +3,15 @@
 # ONOS command-line client
 # -----------------------------------------------------------------------------
 
-export JAVA_HOME=${JAVA_HOME:-/usr/lib/jvm/java-7-openjdk-amd64/}
+if [ -z "${JAVA_HOME}" ]; then
+    if [ -x /usr/libexec/java_home ]; then
+        export JAVA_HOME=$(/usr/libexec/java_home -v 1.8)
+    elif [ -d /usr/lib/jvm/java-8-oracle ]; then
+        export JAVA_HOME="/usr/lib/jvm/java-8-oracle"
+    elif [ -d /usr/lib/jvm/java-7-openjdk-amd64 ]; then
+        export JAVA_HOME="/usr/lib/jvm/java-7-openjdk-amd64"
+    fi
+fi
 
 cd $(dirname $0)/../apache-karaf-$KARAF_VERSION/bin
 ./client -h localhost -u karaf "$@"