util: Remove '\n' from vhostuser ifname

util: Remove '\n' from vhostuser ifname

When deleting the vhostuserclient interface, OVS prompts that the interface does not exist,
Through the XML file, I found that the "target dev" has a '\n', results in an XML parsing error.

XML file:

<target dev='vm-20ac9c030a47
'/>

That is because 'ovs-vsctl' returns a newline result, always come with a '\n',
and the vircommandrun function puts it in ifname.

So virNetDevOpenvswitchGetVhostuserIfname should remove '\n' from ifname.

Signed-off-by: Yalei Li <liyl43@chinatelecom.cn>
Reviewed-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>