qemu: Tear down the cgroup before reattach device to host

qemu: Tear down the cgroup before reattach device to host

When a hostdev is attached to the guest (and removed from the host),
the order of operations is call qemuHostdevPreparePCIDevices to remove
the device from the host, call qemuSetupHostdevCgroup to setup the cgroups,
and virSecurityManagerSetHostdevLabel to set the labels.

When the device is removed from the guest, the code didn't use the
reverse order leading to possible issues (especially if the path to
the device no longer exists). This patch will move the call to
qemuTeardownHostdevCgroup to prior to reattaching the device to
the host.