Remove dhcp/dns configuration from VR, when VM is being DETACHED from a network #3706
Description
As part of the additional cleanup discussed in #3627,
we also need to remove all DHCP/DNS config data (and the active lease) from VR when VM is being DETACHED from a network (any network)
Reason: we need to do the same dhcp/dns config cleanup (that we otherwise do only when VM is being expunged) when we detach network from a VM - since after VM is detached, its reference(s) to its previous network(s) is lost and will never be later cleaned up (dhcp/dns config) when VM is destroyed/expunged later.
Multiple consequences (with multihomed VMs) can be seen if this is not fixed.
@weizhouapache @rhtyd