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

Co-authored-by: Windham Wong <windham.wong@stormeye.io>
diff --git a/heron/packing/src/java/org/apache/heron/packing/roundrobin/RoundRobinPacking.java b/heron/packing/src/java/org/apache/heron/packing/roundrobin/RoundRobinPacking.java
index bbbad2a..a74608d 100644
--- a/heron/packing/src/java/org/apache/heron/packing/roundrobin/RoundRobinPacking.java
+++ b/heron/packing/src/java/org/apache/heron/packing/roundrobin/RoundRobinPacking.java
@@ -102,7 +102,7 @@
 
   @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);