Move downloads to the beginning of the Dockerfile

Hadoop configuration change much faster because doesn't need to download native support each time.

Dockerfile

@@ -29,6 +29,10 @@ RUN rm jdk-7u71-linux-x64.rpm
 ENV JAVA_HOME /usr/java/default
 ENV PATH $PATH:$JAVA_HOME/bin
 
+# download native support
+RUN mkdir -p /tmp/native
+RUN curl -Ls http://dl.bintray.com/sequenceiq/sequenceiq-bin/hadoop-native-64-2.7.0.tar | tar -x -C /tmp/native
+
 # hadoop
 RUN curl -s http://www.eu.apache.org/dist/hadoop/common/hadoop-2.7.0/hadoop-2.7.0.tar.gz | tar -xz -C /usr/local/
 RUN cd /usr/local && ln -s ./hadoop-2.7.0 hadoop
@@ -59,8 +63,8 @@ ADD yarn-site.xml $HADOOP_PREFIX/etc/hadoop/yarn-site.xml
 RUN $HADOOP_PREFIX/bin/hdfs namenode -format
 
 # fixing the libhadoop.so like a boss
-RUN rm /usr/local/hadoop/lib/native/*
-RUN curl -Ls http://dl.bintray.com/sequenceiq/sequenceiq-bin/hadoop-native-64-2.7.0.tar | tar -x -C /usr/local/hadoop/lib/native/
+RUN rm -rf /usr/local/hadoop/lib/native
+RUN mv /tmp/native /usr/local/hadoop/lib
 
 ADD ssh_config /root/.ssh/config
 RUN chmod 600 /root/.ssh/config