Update apt_pre-download script

Refactor apt_pre-download script to classify the packages as per the
services and nodes for better debugging. This change makes it much
more convinent to go through the apt_pre-download.sh for adding,
debugging the issues.

Change-Id: I49f16953805a5895b813abfda2a33775c54236fc

labs/scripts/apt_pre-download.sh

@@ -14,10 +14,46 @@ if [ ! -f "$IMG_DIR/$(basename "$CIRROS_URL")" ]; then
     wget --directory-prefix="$IMG_DIR" "$CIRROS_URL"
 fi
 
+function apt_download {
+
+    sudo apt-get install -y --download-only "$@"
+
+}
+
 # Download packages for all nodes
-sudo apt-get install -y --download-only cinder-api cinder-scheduler lvm2 \
-    cinder-volume glance openstack-dashboard memcached keystone \
-    neutron-server neutron-plugin-ml2 nova-api nova-cert nova-conductor \
-    nova-consoleauth nova-novncproxy nova-scheduler python-novaclient \
-    nova-compute-qemu libguestfs-tools python-guestfs neutron-common \
+
+# MySQL, RabbitMQ
+apt_download mysql-server python-mysqldb rabbitmq-server
+
+# Keystone
+apt_download keystone
+
+# Glance
+apt_download glance
+
+# Nova Controller
+apt_download nova-api nova-cert nova-conductor nova-consoleauth \
+    nova-novncproxy nova-scheduler python-novaclient
+
+# Neutron Controller
+apt_download neutron-server neutron-plugin-ml2
+
+# Cinder Controller
+apt_download cinder-api cinder-scheduler
+
+# Horizon
+apt_download openstack-dashboard memcached
+
+# Cinder Volumes
+apt_download lvm2 cinder-volume
+
+# Nova Compute
+apt_download nova-compute-qemu python-guestfs libguestfs-tools
+
+# Neutron Compute
+apt_download neutron-common neutron-plugin-ml2 \
+    neutron-plugin-openvswitch-agent
+
+# Neutron Network
+apt_download neutron-common neutron-plugin-ml2 \
     neutron-plugin-openvswitch-agent neutron-l3-agent neutron-dhcp-agent