[xenserver|docs] Added new example that covers a Citrix KB ctx116324 article

Translated http://support.citrix.com/article/ctx116324 to fog/xenserver

lib/fog/xenserver/examples/chage_default_storage_repository.md

@@ -0,0 +1,99 @@
+# How To Change the Default Storage Repository to File-based VHD-on-EXT3 
+
+**NOTE: Requires fog > 1.8 (currently in development as of this writing)**
+
+This tutorial explains how to convert a local Logical Volume Manager (LVM) 
+based storage repository into a file-based (VHD) storage repository.
+
+It's the fog/xenserver version of the original Citrix KB article:
+
+http://support.citrix.com/article/ctx116324
+
+To create this tutorial, I've used a vanilla XCP 1.6 ISO install in VirtualBox.
+
+## Create the connection
+
+```ruby
+require 'fog'
+
+conn = Fog::Compute.new({
+  :provider => 'XenServer',
+  :xenserver_url => '192.168.1.39',
+  :xenserver_username => 'root',
+  :xenserver_password => 'secret'
+})
+```
+
+## Remove the LVM-backed storage repository (SR).
+
+Find the default LVM storage repository:
+
+```ruby
+#
+# Equivalent to:
+# xe sr-list type=lvm
+#
+lvm_sr = nil 
+conn.storage_repositories.each do |sr|
+  lvm_sr = sr if sr.type == 'lvm'
+end
+```
+
+Determine the UUID for your default SR's physical block device:
+
+```ruby
+#
+# Equivalent to:
+# xe pbd-list sr-uuid=your SR UUID
+#
+if lvm_sr
+  conn.pbds.each do |pbd|
+    # Unplug it if found
+    # Equivalent to:
+    # xe pbd-unplug uuid=your PBD UUID
+    #
+    pbd.unplug if pbd.storage_repository.uuid == lvm_sr.uuid
+  end
+  # Destroy the SR
+  lvm_sr.destroy 
+end
+```
+
+Create a new VHD-backed SR:
+
+```ruby
+#
+# Equivalent to:
+#
+# xe sr-create content-type="local SR" \
+#              host-uuid=5d189b7a-cd5e-4029-9940-d4daaa34633d \ 
+#              type=ext device-config-device=/dev/sda3 shared=false \
+#              name-label="Local File SR"
+#
+sr = conn.storage_repositories.create :name => 'Local File SR',
+                                      :host => conn.hosts.first,
+                                      :type => 'ext',
+                                      :content_type => 'local SR',
+                                      :device_config => { :device => '/dev/sda3' },
+                                      :shared => false
+```
+
+Set your SR as the default SR on the system:
+
+```ruby
+#
+# Equivalent command:
+# xe pool-param-set suspend-image-SR='YOUR NEW SR UUID' uuid=bleh
+#
+conn.pools.first.default_storage_repository = sr
+```
+
+Set your SR as the default location for suspended VM images:
+
+```ruby
+#
+# Equivalent command:
+# xe pool-param-set suspend-image-SR= YOUR NEW SR UUID  uuid=bleh
+#
+conn.pools.first.suspend_image_sr = sr
+```