[xenserver|docs] added storage repositories examples

lib/fog/xenserver/examples/storage_repositories.md

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+# Storage Repositories
+
+Official storage repository Citrix API documentation:
+
+http://docs.vmd.citrix.com/XenServer/6.0.0/1.0/en_gb/api/?c=SR
+
+Create the XenServer connection first, as usual:
+
+    require 'fog'                                                               
+    require 'net/scp'
+    require 'pp'
+    
+    xenserver = Fog::Compute.new({
+      :provider => 'XenServer',
+      :xenserver_url => 'xenserver-test',
+      :xenserver_username => 'root',
+      :xenserver_password => 'secret',
+    })
+
+
+Listing the available storage repositories 
+
+    xenserver.storage_repositories
+
+
+Filter storage repositories by content type:
+
+    xenserver.storage_repositories.select { |sr| sr.content_type == 'iso' }
+
+Filter storage repositories by allowed operations:
+
+    rw_srs = xenserver.storage_repositories.select do |sr| 
+      # Are we allowed to create a VDI here?
+      sr.allowed_operations.include? 'vdi_create'
+    end
+
+Print some attributes of the first SR found:
+
+    sr = rw_srs.first
+    puts sr.name
+    puts sr.description
+    puts sr.type
+    puts sr.tags
+    # in bytes
+    puts sr.physical_size
+    puts sr.physical_utilisation
+    # sum of virtual_sizes of all VDIs in this storage repository (in bytes)
+    puts sr.virtual_allocation
+
+ 
+List virtual disk images available and print some VDI's attributes:
+
+    sr.vdis.each do |vdi|
+      # http://docs.vmd.citrix.com/XenServer/6.0.0/1.0/en_gb/api/?c=VDI
+      puts vdi.uuid
+      puts vdi.is_a_snapshot
+      puts vdi.name
+      # in bytes
+      puts vdi.physical_utilisation
+      puts vdi.virtual_size
+      puts vdi.read_only
+      # ["update", "resize", "destroy", "clone", "copy", "snapshot"],
+      puts vdi.allowed_operations 
+    end
+
+Create a new VDI in this storage repository:
+
+    vdi = xenserver.vdis.create :name => 'super-vdi',                                       
+                                :storage_repository => sr,                               
+                                :description => 'my super-vdi',                             
+                                :virtual_size => '1073741824' # 1 GB
+
+I have an ext3 storage repository and this creates a 1GB VHD file there:
+
+    [root@xenserver ~]# vhd-util query -v -n /var/run/sr-mount/6edd263a-2da1-7533-840c-768417b5be25/4050057d-a3a8-4c00-8f2e-cf5531232921.vhd
+    1024
+
+Destroy it
+
+    vdi.destroy