libfdisk: use fdisk_table to generate output

libfdisk: use fdisk_table to generate output

 * add generic fdisk_iter iterator
 * use fdisk_table to convert partition table to human readable output
 * clean up partition.c API (don't use reference to fdisk_context in
   fdisk_partition struct)
 * extern table.c API to use fdisk_iter iterator
 * remove old fdisk_list_partitions()

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