selinux: allow dpdkvhostuserclient sockets with newer libvirt

selinux: allow dpdkvhostuserclient sockets with newer libvirt

Newer libvirt and openstack versions will now label the unix socket as
an `svirt_tmpfs_t` object.  This means that in order to support
deploying with the recommended configuration (using a
dpdkvhostuserclient socket), additional permissions need to be
installed as part of the selinux policy.

An example of some of the AVC violations:

    type=AVC msg=audit(1518752799.102:978): avc:  denied  { write }
    for  pid=14368 comm="ovs-vswitchd" name="vhost0" dev="dm-0" ino=94
    scontext=system_u:system_r:openvswitch_t:s0
    tcontext=system_u:object_r:svirt_tmp_t:s0 tclass=sock_file

    type=AVC msg=audit(1518816172.126:1318): avc:  denied  { connectto }
    for  pid=32717 comm="ovs-vswitchd" path="/tmp/vhost0"
    scontext=system_u:system_r:openvswitch_t:s0
    tcontext=system_u:system_r:svirt_t:s0:c106,c530
    tclass=unix_stream_socket

Signed-off-by: Aaron Conole <aconole@redhat.com>
Acked-by: Ansis Atteka <aatteka@ovn.org>