Set HDFS replication factor 1 in dev and tests

Only one datanode runs in spark local development and tests, therefore, set
the replication factor to 1 to avoid the namenode from complaining about
under-replicated blocks.

Author: amCap1712

docker/spark-cluster-config/test/hdfs-site.xml

@@ -25,4 +25,8 @@
         <name>dfs.datanode.data.dir</name>
         <value>file:///hdfs/datanode</value>
     </property>
+    <property>
+      <name>dfs.replication</name>
+      <value>1</value>
+    </property>>
 </configuration>