For command line we need two things:

1) -object pr-manager-helper,id=$alias,path=$socketPath
2) -drive file.pr-manager=$alias

In -object pr-manager-helper we tell qemu which socket to connect
to, then in -drive file-pr-manager we just reference the object
the drive in question should use.

For managed PR helper the alias is always "pr-helper0" and socket
path "${vm->priv->libDir}/pr-helper0.sock".
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>