Automatically remove invalid file characters for disk name

This commit copies what Vagrant does to filter out guest names with
invalid characters, and applies the same regex to disk names.

plugins/kernel_v2/config/disk.rb

@@ -12,6 +12,8 @@ module VagrantPlugins
 
       DEFAULT_DISK_TYPES = [:disk, :dvd, :floppy].freeze
 
+      FILE_CHAR_REGEX = /[^-a-z0-9_]/i.freeze
+
       # Note: This value is for internal use only
       #
       # @return [String]
@@ -115,7 +117,10 @@ module VagrantPlugins
           @primary = false
         end
 
-        if @name == UNSET_VALUE
+        if @name.is_a?(String) && @name.match(FILE_CHAR_REGEX)
+            @logger.warn("Vagrant will remove detected invalid characters in '#{@name}' and convert the disk name into something usable for a file")
+            @name.gsub!(FILE_CHAR_REGEX, "")
+        elsif @name == UNSET_VALUE
           if @primary
             @name = "vagrant_primary"
           else