Same problem.

virt-manager --debug:
[Ср, 23 май 2018 12:17:53 virt-manager 9023] DEBUG (guest:248) Setting Guest.os_variant to 'generic'
[Ср, 23 май 2018 12:17:53 virt-manager 9023] DEBUG (distroinstaller:191) Error validating install location
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtinst/distroinstaller.py", line 186, in _validate_location
    dev.path = val
  File "/usr/share/virt-manager/virtinst/devicedisk.py", line 511, in _set_path
    self._set_xmlpath(self.path)
  File "/usr/share/virt-manager/virtinst/devicedisk.py", line 712, in _set_xmlpath
    if self._storage_backend.get_dev_type() == "network":
  File "/usr/share/virt-manager/virtinst/diskbackend.py", line 600, in get_dev_type
    self._conn.is_remote())
  File "/usr/share/virt-manager/virtinst/diskbackend.py", line 203, in _get_dev_type

uname -a
Linux adm2 4.4.0-127-generic #153-Ubuntu SMP Sat May 19 10:58:46 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux


    if vol_xml.file_type == libvirt.VIR_STORAGE_VOL_BLOCK:
  File "/usr/share/virt-manager/virtinst/storage.py", line 717, in _get_vol_type
    return self._pool_xml.get_disk_type()
AttributeError: 'NoneType' object has no attribute 'get_disk_type'
[Ср, 23 май 2018 12:17:53 virt-manager 9023] ERROR (error:142) Ошибка валидации: Ошибка при выборе расположения установочного носителя. Validating install media '/data/iso/zentyal-3.2-amd64.iso' failed: 'NoneType' object has no attribute 'get_disk_type'
Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/create.py", line 1820, in _validate_install_page
    self._guest.installer.location = location
  File "/usr/share/virt-manager/virtinst/installer.py", line 80, in set_location
    self._location = self._validate_location(val)
  File "/usr/share/virt-manager/virtinst/distroinstaller.py", line 193, in _validate_location
    (str(val), e))
ValueError: Validating install media '/data/iso/zentyal-3.2-amd64.iso' failed: 'NoneType' object has no attribute 'get_disk_type'

dpkg -l | grep qemu
rc  aqemu                                                       0.8.2-2build1                                               amd64        Qt4 front-end for QEMU and KVM
ii  ipxe-qemu                                                   1.0.0+git-20150424.a25a16d-1ubuntu1.2                       all          PXE boot firmware - ROM images for qemu
ii  qemu                                                        1:2.5+dfsg-5ubuntu10.29                                     amd64        fast processor emulator
ii  qemu-block-extra:amd64                                      1:2.5+dfsg-5ubuntu10.29                                     amd64        extra block backend modules for qemu-system and qemu-utils
ii  qemu-kvm                                                    1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU Full virtualization
ii  qemu-slof                                                   20151103+dfsg-1ubuntu1.1                                    all          Slimline Open Firmware -- QEMU PowerPC version
ii  qemu-system                                                 1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries
ii  qemu-system-arm                                             1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (arm)
ii  qemu-system-common                                          1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (common files)
ii  qemu-system-mips                                            1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (mips)
ii  qemu-system-misc                                            1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (miscelaneous)
ii  qemu-system-ppc                                             1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (ppc)
ii  qemu-system-sparc                                           1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (sparc)
ii  qemu-system-x86                                             1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU full system emulation binaries (x86)
ii  qemu-user                                                   1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU user mode emulation binaries
ii  qemu-user-binfmt                                            1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU user mode binfmt registration for qemu-user
ii  qemu-utils                                                  1:2.5+dfsg-5ubuntu10.29                                     amd64        QEMU utilities

dpkg -s virt-manager
Version: 1:1.4.1-1~getdeb1


Installing qemu-kvm, qemu-kmv-tools, qemu-system don't help. I tried to downgrade virt-manager to 1.1.1.3 - don't help too.