[SYSTEMDS-3476] Spark with default settings

There was a bug in the /bin/systemds script that did not properly
set up the spark execution variables with default variables.
1. bug was memory was set to 16 not 16g, 2. was the log4j variable
that was overwritten and used incorrectly.

Both bugs are fixed, but there could be use of some more cleanup of our
/bin/systemds script.

Closes apache#1748

bin/systemds

@@ -107,6 +107,8 @@ else
   LOG4JPROP2=$(find "$LOG4JPROP")
   if [ -z "${LOG4JPROP2}" ]; then
     LOG4JPROP=""
+  elif [ -z "${SYSTEMDS_DISTRIBUTED_OPTS}" ]; then
+    LOG4JPROP=$LOG4JPROP
   else
     LOG4JPROP="-Dlog4j.configuration=file:$LOG4JPROP2"
   fi
@@ -126,7 +128,7 @@ else
       --files $LOG4JPROP \
       --conf spark.network.timeout=512s \
       --num-executors 4 \
-      --executor-memory 64 \
+      --executor-memory 64g \
       --executor-cores 16 "
 fi