fdisk: (gpt) add t, v and x to menu

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: remove unnecessary code from test_fdisk_ask

.. 'sun' stuff is already in the library.

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: make the library usable with tests

We don't have completely initialized all label drivers in the tests, so
make the code more robust.

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: add new stuff to display menus

fdisk menus:

 - driven by menu and menu_entry structs
 - supports normal and expect mode
 - supports multiple independent menus
 - supports menu separators to make output more readable
 - allows to exclude by whole menu or menu entries by label type

TODO:
 - define per label menus
 - per menu callback
 - sensitive only to keys defined in the currently printed menu

Signed-off-by: Karel Zak <kzak@redhat.com>