[xapi]: during Pool.join, when importing VM metadata, omit the control domain
[xapi]: during Pool.join, when importing VM metadata, omit the control domain

This avoids glitches where the control domain ends up Halted and not resident_on
the right host. An alternative solution would be to add Hosts to the metadata
import/export.

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>

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