fix fedora19 chef rubygems issue

fixes:
```bash
$ veewee vbox validate fedora-19-x86_64
...
Checking chef - FAILED
Command: . /etc/profile ;chef-client --version 2> /dev/null 1>/dev/null; echo $?
Expected string 0
Output: 
```
=>
```bash
$ chef-client --version
/usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require': cannot load such file -- rubygems/format (LoadError)
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/local/share/gems/gems/chef-11.4.4/lib/chef/provider/package/rubygems.rb:34:in `<top (required)>'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/local/share/gems/gems/chef-11.4.4/lib/chef/providers.rb:60:in `<top (required)>'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/local/share/gems/gems/chef-11.4.4/lib/chef.rb:25:in `<top (required)>'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:45:in `require'
	from /usr/local/share/gems/gems/chef-11.4.4/bin/chef-client:23:in `<top (required)>'
	from /usr/local/bin/chef-client:23:in `load'
	from /usr/local/bin/chef-client:23:in `<main>'
```