[COOK-3341] frequency and rotate params are optional in app conf when defined globally

see http://tickets.opscode.com/browse/COOK-3341

When defined in the global config file, frequency and rotate values do not have to be passed to logrotate_app definition. The global values would be used if omitted.

And if these two params are omitted, the app config file should not include them. Otherwise the
config file is invalid.

___

_A side question, for the Chef experts:_

The `logrotate_app` definition describes [a few parameters](https://github.com/opscode-cookbooks/logrotate/blob/master/definitions/logrotate_app.rb#L20):
:frequency, :template, :cookbook, :postrotate, etc

However a few others are used in the definition [implementation](https://github.com/opscode-cookbooks/logrotate/blob/master/definitions/logrotate_app.rb#L47): :minsize, :create, :olddir

Obviously it works just fine but is there any reason for these "hidden" parameters? or is it a simple mistake?

thanks,

Alexis