Nova skips detaching of ovs dpdk interfaces
thinking that it's already detached because
get_interface_by_cfg() return no inteface.
This is due to _set_config_VIFVHostUser()
not setting target_dev in configuration while
LibvirtConfigGuestInterface sets target_dev
if tag "target" is found in the interface.
As target_dev is not a valid value for
vhostuser interface, it will not be checked
for vhostuser type.
Change-Id: Iaf185b98c236df47e44cda0732ee0aed1fd6323d
Closes-Bug: #1807340
(cherry picked from commit a19c38a6ab)
(cherry picked from commit 1ac56a4038)
6d38ba1589