CP-2767: Refactor Xapi_vif.move
CP-2767: Refactor Xapi_vif.move

This patch does not introduce any functionality change, but refactors
out a reusable part of Xapi_vif.move into its own function.

djs55/squeezed,simonjbeaumont/xcp-rrdd,robhoes/squeezed,djs55/xcp-networkd,koushikcgit/xcp-networkd,djs55/xcp-rrdd,sharady/xcp-networkd,djs55/xcp-rrdd,sharady/xcp-networkd,koushikcgit/xcp-rrdd,johnelse/xcp-rrdd,koushikcgit/xcp-rrdd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-rrdd,koushikcgit/xcp-networkd,johnelse/xcp-rrdd,djs55/xcp-networkd