Recognise NBDs (Network Block Devices) (#247)

Network Block Devices are not displayed in GParted as partitionable
devices.  They do appear in /proc/partitions, are reported by
fdisk -l [1] and by ped_device_probe_all() from libparted.  Therefore
include them.

Create NBD device for testing:
    # truncate -s 1G /tmp/disk-1G.img
    # nbd-server -C /dev/null 9000 /tmp/disk-1G.img
    # nbd-client localhost 9000 /dev/nbd0

After creating a couple of partitions for testing, the contents of
/proc/partitions looks like this:
    # egrep 'name|nbd' /proc/partitions
    major minor  #blocks  name
      43        0    1048576 nbd0
      43        1     262144 nbd0p1
      43        2     785408 nbd0p2

Listing all disks using fdisk:
    # fdisk -l
    ...

    Disk /dev/nbd0: 1 GiB, 1073741824 bytes, 2097152 sectors
    Units: sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disklabel type: dos
    Disk identifier: 0x081b1cd1

    Device      Boot  Start     End Sectors  Size Id Type
    /dev/nbd0p1        2048  526335  524288  256M 83 Linux
    /dev/nbd0p2      526336 2097151 1570816  767M 83 Linux

Temporarily apply this patch to GParted so that it ignores the devices it
currently selects from /proc/partitions to use what get_device_probe_all()
reports.  GParted shows NBDs.
    $ git diff --unified=1
    diff --git a/src/GParted_Core.cc b/src/GParted_Core.cc
    index 1629f94f..abea7a0b 100644
    --- a/src/GParted_Core.cc
    +++ b/src/GParted_Core.cc
    @@ -172,3 +172,3 @@ void GParted_Core::set_devices_thread( std::vector<Device> * pdevices )
            //try to find all available devices if devices exist in /proc/partitions
    -       std::vector<Glib::ustring> temp_devices = Proc_Partitions_Info::get_device_paths();
    +       std::vector<Glib::ustring> temp_devices;
            if ( ! temp_devices .empty() )

Tidy-up NBD device:
    # nbd-client -d /dev/ndb0
    # killall nbd-server
    # rm /tmp/disk-1G.img

[1] man fdisk
    "-l, --list
        List the partition tables for the specified devices and then
        exit.  If no devices are given, the devices mentioned in
        /proc/partitions (if this file exists) are used.
    "

Closes #247 - GParted does not list NBD (Network Block Device) devices
              in the GUI

src/Proc_Partitions_Info.cc

@@ -160,6 +160,11 @@ bool Proc_Partitions_Info::is_whole_disk_device_name(const Glib::ustring& name)
 	if (Utils::regexp_label(name, "^(bcache[0-9]+)$") != "")
 		return true;
 
+	// Match Network Block Device names.
+	// E.g.: device = nbd0 (partition = nbd0p1)
+	if (Utils::regexp_label(name, "^(nbd[0-9]+)$") != "")
+		return true;
+
 	return false;
 }