Support separate storage pools for additional disks (#1130)

Add support for a pool setting for additional disks, example:

Vagrant.configure("2") do |config|
  config.vm.box = "generic/centos8"
    config.vm.provider :libvirt do |domain|
        domain.storage :file, :size => '20G', :pool=>'default'
        domain.snapshot_pool_name='cache'
    end
end

this allows to place the virtual machines snapshot in the "cache" pool,
while additional disks are created in the "default" storage pool.

lib/vagrant-libvirt/action/create_domain.rb

@@ -151,10 +151,7 @@ module VagrantPlugins
             if env[:machine].config.vm.box
               storage_prefix = File.dirname(@domain_volume_path) + '/' # steal
             else
-              storage_pool = env[:machine].provider.driver.connection.client.lookup_storage_pool_by_name(@storage_pool_name)
-              raise Errors::NoStoragePool if storage_pool.nil?
-              xml = Nokogiri::XML(storage_pool.xml_desc)
-              storage_prefix = xml.xpath('/pool/target/path').inner_text.to_s + '/'
+              storage_prefix = get_disk_storage_prefix(env, @storage_pool_name)
             end
           end
 
@@ -169,6 +166,16 @@ module VagrantPlugins
 
             disk[:absolute_path] = storage_prefix + disk[:path]
 
+            if not disk[:pool].nil?
+              disk_pool_name = disk[:pool]
+              @logger.debug "Overriding pool name with: #{disk_pool_name}"
+              disk_storage_prefix = get_disk_storage_prefix(env, disk_pool_name)
+              disk[:absolute_path] = disk_storage_prefix + disk[:path]
+              @logger.debug "Overriding disk path with: #{disk[:absolute_path]}"
+            else
+              disk_pool_name = @storage_pool_name
+            end
+
             # make the disk. equivalent to:
             # qemu-img create -f qcow2 <path> 5g
             begin
@@ -178,7 +185,7 @@ module VagrantPlugins
                 path: disk[:absolute_path],
                 capacity: disk[:size],
                 #:allocation => ?,
-                pool_name: @storage_pool_name
+                pool_name: disk_pool_name
               )
             rescue Libvirt::Error => e
               # It is hard to believe that e contains just a string
@@ -366,6 +373,14 @@ module VagrantPlugins
 
           @app.call(env)
         end
+
+        private
+        def get_disk_storage_prefix(env, disk_pool_name)
+          disk_storage_pool = env[:machine].provider.driver.connection.client.lookup_storage_pool_by_name(disk_pool_name)
+          raise Errors::NoStoragePool if disk_storage_pool.nil?
+          xml = Nokogiri::XML(disk_storage_pool.xml_desc)
+          disk_storage_prefix = xml.xpath('/pool/target/path').inner_text.to_s + '/'
+        end
       end
     end
   end

lib/vagrant-libvirt/config.rb

@@ -605,7 +605,8 @@ module VagrantPlugins
           allow_existing: options[:allow_existing],
           shareable: options[:shareable],
           serial: options[:serial],
-          wwn: options[:wwn]
+          pool: options[:pool], # overrides storage_pool setting for additional disks
+          wwn: options[:wwn],
         }
 
         @disks << disk # append