Added fluent interface support for shared matchers. 

Similar to existing one in remote_file.
Now one can write one line tests like that:

    should create_user( 'tomcat' ).with :system => true, :shell => '/bin/false'

Instead of:

    should create_user( 'tomcat' )
    user( 'tomcat' ).system.should == true
    user( 'tomcat' ).shell.should == '/bin/false'

And that's not only with user, but any other matcher that's created with define_resource_matchers in shared.rb