Description of problem:
V2V fails to convert VM with >=4 virtio devices.

#virsh dumpxml kvm-rhel6.1-i386-4vdXX
...
 <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/mnt/sdb/image/kvm-rhel6.1-i386-4vdXX'/>
      <target dev='vda' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <source file='/mnt/sdb/image/kvm-rhel6.1-i386-4vdXX-disk2.img'/>
      <target dev='vdb' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <source file='/mnt/sdb/image/kvm-rhel6.1-i386-4vdXX-disk4.img'/>
      <target dev='vdc' bus='virtio'/>
    </disk>
    <disk type='file' device='disk'>
      <source file='/mnt/sdb/image/kvm-rhel6.1-i386-4vdXX-disk3.img'/>
      <target dev='vdd' bus='virtio'/>
    </disk>
...



Version-Release number of selected component (if applicable):
virt-v2v-0.7.1-4.el6.x86_64
libguestfs-1.7.17-15.el6.x86_64
libvirt-0.8.7-6.el6.x86_64
qemu-kvm-0.12.1.2-2.135.el6.x86_64

How reproducible:
always

Steps to Reproduce:
1. Convert the VM with 4 virtio devices
# LIBGUESTFS_DEBUG=1 virt-v2v -ic qemu+ssh://10.66.72.122/system  -o rhev -op 10.66.90.115:/vol/v2vrwu1/rwu_export kvm-rhel6.1-i386-4vdXX
kvm-rhel6.1-i386-4vdXX: 100% [=========================================================================]D 0h02m12s
kvm-rhel6.1-i386-4vdXX-disk2.img: 100% [===============================================================]D 0h01m07s
kvm-rhel6.1-i386-4vdXX-disk4.img: 100% [===============================================================]D 0h01m08s
kvm-rhel6.1-i386-4vdXX-disk3.img: 100% [===============================================================]D 0h01m07s
new guestfs handle 0x2dc94b0
[00000ms] febootstrap-supermin-helper --verbose -u 36 -g 36 -f checksum '/usr/lib64/guestfs/supermin.d' x86_64
supermin helper [00000ms] whitelist = (not specified), host_cpu = x86_64, kernel = (null), initrd = (null), appliance = (null)
supermin helper [00000ms] inputs[0] = /usr/lib64/guestfs/supermin.d
checking modpath /lib/modules/2.6.32-71.el6.x86_64 is a directory
picked vmlinuz-2.6.32-71.el6.x86_64 because modpath /lib/modules/2.6.32-71.el6.x86_64 exists
supermin helper [00000ms] finished creating kernel
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/base.img
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/daemon.img
supermin helper [00000ms] visiting /usr/lib64/guestfs/supermin.d/hostfiles
supermin helper [00011ms] visiting /usr/lib64/guestfs/supermin.d/ntfs.hostfiles
supermin helper [00011ms] visiting /usr/lib64/guestfs/supermin.d/ntfs.img
supermin helper [00075ms] finished creating appliance
[00080ms] begin testing qemu features
[00098ms] finished testing qemu features
[00100ms] /usr/libexec/qemu-kvm \
    -drive file=/tmp/mjUop0LTIi/ee84623f-0ded-4144-adf2-69bed2e69732/v2v.0fCZ8L97/14f5b67a-8180-48a0-91e9-6185cacf6a1f/ccbc949d-71b9-4d3d-84cc-5b8ff098e3c4,cache=off,if=ide \
    -drive file=/tmp/mjUop0LTIi/ee84623f-0ded-4144-adf2-69bed2e69732/v2v.0fCZ8L97/f582e314-13fb-40eb-b25d-f412b97b0f03/fda0020b-8df1-4810-9486-23bf9aea5926,cache=off,if=ide \
    -drive file=/tmp/mjUop0LTIi/ee84623f-0ded-4144-adf2-69bed2e69732/v2v.0fCZ8L97/c21ca91d-27ab-4b80-aaff-b369765ae8f2/37988862-0842-43e6-a90e-3f3a52565888,cache=off,if=ide \
    -drive file=/tmp/mjUop0LTIi/ee84623f-0ded-4144-adf2-69bed2e69732/v2v.0fCZ8L97/d66950cf-b83a-4d1b-9f1e-484994b8dc7d/47de6f46-1276-4c84-9e55-d4b55b0b8f53,cache=off,if=ide \
    -drive file=/var/lib/virt-v2v/transfer.iso,snapshot=on,if=ide \
    -nodefconfig \
    -enable-kvm \
    -nodefaults \
    -nographic \
    -m 500 \
    -no-reboot \
    -device virtio-serial \
    -serial stdio \
    -chardev socket,path=/tmp/libguestfsGpprEU/sock,id=channel0 \
    -device virtserialport,chardev=channel0,name=org.libguestfs.channel.0 \
    -netdev user,id=usernet,net=169.254.0.0/16 \
    -device virtio-net-pci,netdev=usernet \
    -kernel /tmp/.guestfs-36/kernel.19020 \
    -initrd /tmp/.guestfs-36/initrd.19020 \
    -append 'panic=1 console=ttyS0 udevtimeout=300 noapic acpi=off printk.time=1 cgroup_disable=memory selinux=0 guestfs_verbose=1 TERM=xterm ' \
    -drive file=/tmp/.guestfs-36/root.19020,snapshot=on,if=virtio,cache=unsafe
accept_from_daemon: 0x2dc94b0 g->state = 1
recv_from_daemon: 0x2dc94b0 g->state = 1, size_rtn = 0x7fff0a6f297c, buf_rtn = 0x7fff0a6f2940
qemu: too many IDE bus
child_cleanup: 0x2dc94b0: child process died
unexpected end of file when reading from daemon at /usr/share/perl5/vendor_perl/Sys/VirtV2V/GuestfsHandle.pm line 86.
closing guestfs handle 0x2dc94b0 (state 0)

  
Actual results:
Fail to convert VM with >=4 virtio devices

Expected results:
Convert successfully.

Additional info:
I guess the reason is there is no conditional statement to get the interface instead of a fix "ide" in GuestfsHandle.pm:
#cat /usr/share/perl5/vendor_perl/Sys/VirtV2V/GuestfsHandle.pm
...
sub new
{
    my $class = shift;
    my ($storage, $transfer, $isrhev) = @_;

    my $self = {};

    # Open a guest handle
    my $g;
    my $open = sub {
        my $interface = "ide";

        $g = open_guest($storage, rw => 1, interface => $interface);

        # Add the transfer iso if there is one
        $g->add_drive_ro_with_if($transfer, $interface) if (defined($transfer));

        # Enable networking in the guest
        $g->set_network(1);

        $g->launch();
    };