Decrease the minimum requirement of RAM of single instance to 16MB in Round Robin algorithm (#3678)

Co-authored-by: Windham Wong <[email protected]>

Author: windhamwong

heron/packing/src/java/org/apache/heron/packing/roundrobin/RoundRobinPacking.java

@@ -102,7 +102,7 @@ public class RoundRobinPacking implements IPacking, IRepacking {
 
   @VisibleForTesting
   static final ByteAmount DEFAULT_DAEMON_PROCESS_RAM_PADDING = ByteAmount.fromGigabytes(1);
-  private static final ByteAmount MIN_RAM_PER_INSTANCE = ByteAmount.fromMegabytes(192);
+  private static final ByteAmount MIN_RAM_PER_INSTANCE = ByteAmount.fromMegabytes(16);
 
   // Use as a stub as default number value when getting config value
   private static final ByteAmount NOT_SPECIFIED_BYTE_AMOUNT = ByteAmount.fromBytes(-1);