Fixup disk config parsing to allow hash and block

plugins/kernel_v2/config/disk.rb

@@ -84,7 +84,7 @@ module VagrantPlugins
 
         current = @config_class.new
         current.set_options(options) if options
-        block.call(current) if block
+        block.call(current) if block_given?
         current = @config.merge(current) if @config
         @config = current
       end
@@ -121,7 +121,7 @@ module VagrantPlugins
         end
 
         # TODO: Convert a string to int here?
-        if !@size.is_a?(Integer)
+        if @size && !@size.is_a?(Integer)
           errors << "Config option size for disk is not an integer"
         end
 

plugins/kernel_v2/config/vm.rb

@@ -406,12 +406,14 @@ module VagrantPlugins
 
       def disk(type, **options, &block)
         disk = VagrantConfigDisk.new(type)
-        if block.is_a?(Hash)
-          disk.set_options(block)
-        else
+
+        disk.set_options(options)
+
+        if block_given?
           block.call(disk, VagrantConfigDisk)
         end
 
+        # Add provider config
         disk.add_config(options, &block)
 
         @__disks << disk