Rename variable to have DIB_ prefix

Rename the variable CDH_HDFS_ONLY used by the hadoop-cloudera
element to have the DIB_ prefix.

Change-Id: Ib51544f44258c62618c48a7ab6a2b25f804ab89a

diskimage-create/diskimage-create.sh

@@ -473,7 +473,7 @@ if [ -z "$PLUGIN" -o "$PLUGIN" = "spark" ]; then
     fi
 
     # Tell the cloudera element to install only hdfs
-    export CDH_HDFS_ONLY=1
+    export DIB_CDH_HDFS_ONLY=1
 
     export ubuntu_image_name=${ubuntu_spark_image_name:-"ubuntu_sahara_spark_latest"}
 
@@ -485,7 +485,7 @@ if [ -z "$PLUGIN" -o "$PLUGIN" = "spark" ]; then
     disk-image-create $TRACING $ubuntu_elements_sequence -o $ubuntu_image_name
     unset DIB_CLOUD_INIT_DATASOURCES
     unset DIB_HDFS_LIB_DIR
-    unset CDH_HDFS_ONLY
+    unset DIB_CDH_HDFS_ONLY
     unset DIB_CDH_VERSION
     unset DIB_SPARK_VERSION
     unset DIB_HADOOP_VERSION

elements/hadoop-cloudera/README.rst

@@ -23,7 +23,7 @@ Environment Variables
 The element can be configured by exporting variables using a
 `environment.d` script.
 
-CDH_HDFS_ONLY
+DIB_CDH_HDFS_ONLY
   :Required: No
   :Description: If set will install only the namenode and datanode
     packages with their dependencies.

elements/hadoop-cloudera/install.d/50-install-cloudera

@@ -12,7 +12,7 @@ if [ "$DISTRO_NAME" = "ubuntu" ]; then
 fi
 
 # Install the rest of CDH unless a limited HDFS install was requested
-if [ -z "${CDH_HDFS_ONLY:-}" ]; then
+if [ -z "${DIB_CDH_HDFS_ONLY:-}" ]; then
     install-packages \
         cloudera-manager-agent \
         cloudera-manager-daemons \