Improve the doc for building the iso in a vm

- more generic doc (address both virtualbox and vagrant)

- suggest how to use the more reliable docker's aufs storage backend

Closes-Bug: #1527656
Change-Id: I825848a8e715f08e3f6ac342d745d4633f87d992

docs/develop/env.rst

@@ -134,12 +134,43 @@ your Fuel ISO build environment on Ubuntu 14.04:
     make clean          #remove build/ directory
     make deep_clean     #remove build/ and local_mirror/
 
-.. note:: In case you are using Virtualbox for building iso, please ensure that the build
-    directory BUILD_DIR and LOCAL_MIRROR
-    (see `config.mk <https://github.com/openstack/fuel-main/blob/master/config.mk>`_)
-    both ``are OUT`` of the Virtualbox
-    `shared folder path <https://www.virtualbox.org/manual/ch04.html#sharedfolders>`_
+.. note::
 
+  In case you use a virtual machine for building the image, verify the
+  following:
+
+    - Both ``BUILD_DIR`` and ``LOCAL_MIRROR`` build directories are
+      out of the shared folder path in the `config.mk
+      <https://github.com/openstack/fuel-main/blob/master/config.mk>`_
+      file. For more information, see:
+
+        - `Shared folders of VitrualBox
+          <https://www.virtualbox.org/manual/ch04.html#sharedfolders>`_
+          documentation
+
+        - `Synced folders of Vargant
+          <https://docs.vagrantup.com/v2/synced-folders/>`_
+          documentation
+
+    - To prevent a random docker unexpected termination, a virtual
+      machine has a kernel that supports the ``aufs`` file system.
+
+      To install the kernel, run:
+
+      .. code-block:: console
+
+        sudo apt-get install --yes linux-image-extra-virtual
+
+      Reboot the kernel when the installation is complete.  Check that
+      docker is using ``aufs`` by running:
+
+      .. code-block:: console
+
+        sudo docker info 2>&1 | grep -q 'Storage Driver: aufs' \
+	&& echo OK || echo KO
+
+      For more information, see `Select a storage driver for docker
+      <https://docs.docker.com/engine/userguide/storagedriver/selectadriver/>`_.
 
 You can also use the following tools to make your work and development process
 with Fuel easier: