install-chef-suse: Add use_dialog to know if dialog should be called

This makes it easier to change the checks to determine if dialog should
be used or not. And one new check is that --verbose is not used: in
verbose mode, dialog was only used for the messages at the end, which is
not wanted.
Merge pull request #1838 from vuntz/install-chef-suse-no-verbose-dialog

install-chef-suse: Add use_dialog to know if dialog should be called