This avoids unnecessary udev events, which in some cases were causing
udevd to trigger a kernel partition table reread, causing the kernel
to get out of sync with drakx.

In order to do so, the libparted bindings are enhanced so that we
manipulate a 'ped_disk' object:
- disk_open() returns such an object
- set_disk_type() is removed
- disk_commit() writes back the partition table and tell the kernel
  about it
  if we fails to write the partition table, we let
  partition_table::write() fire an exceptionc
  if we only have succeed in writing the partition table, we let
  partition_table::write() try harder (umounting partitions before
  trying againt to tell the kernel again)
- need_to_tell_kernel() is overrided

The last change is needed because we now tell the kernel about the new
partition layout in partition_table::gpt::write() when calling
disk_commit() while previously we were deferring that to
partition_table::write() which after having called the gpt's write()
calls tell_kernel() -> c::tell_kernel_to_reread_partition_table()

So we must tell partition_table::write() that telling the kernel to
reread the partition_table is not needed if we already succeeded in
that.

it's unused since commit 1daabebda57976579465e5c281eaa14088e0e37f

Needed for next commit
It could also be later used for drakx's lspci (like for ldetect's
lspcidrake)

it was added in commit 58776de07de819cb962aa35e76c8379d96f03e6b

let's abuse ->{pt_type} for tracking such partitions

...when adding or deleting a partition or setting its flag
rationale: telling kernel to reread partition table is done later in
partition_table::write() whereas partition_table::gpt::write() job is
just to update partition table on disk.

On some machines, calls to ped_disk_new() in libparted take of
the order of seconds, so doing this for each flag and partition
in turn makes partition_table::gpt::read_one take an inordinate
amount of time (mga#15621). Instead, collect the flags during the
call to c::get_disk_partitions.