Add running container to mapped network

[hickeng]

Where #743 adds a bridge network to a running container, this adds mapped vSphere networks that require PCI hotadd of a new vNIC. The workflow in the portlayer should be identical to the pseudo-code in #743. The network.Join operation adding a DeviceChange entry for the new NIC should be invisible to the callers.

On the tether side this requires hotadd and configuration of the new vNIC. This may not require #742 as the hotadd event itself can be used as a trigger, as such I do not consider it a dependency for this work.

[stuclem]

Already in the release notes, so removing the kind/note tag.

[mhagen-vmware]

This is too big to be in the backlog and needs to be decomposed more

[zjs]

In addition to the above, this is blocked by vSphere guestinfo volatility bug (fixed in 6.5U1, possibly backported to a 6.0 update release). This can be considered once we no longer support versions that are impacted by this bug.