Change the function which determines whether to explicitly write zeroes into VDIs during copies and imports.
Change the function which determines whether to explicitly write zeroes into VDIs during copies and imports.

We still default to not writing zeroes (hoping to preserve sparseness) but will write zeroes if:
* SM backend is one of [ lvm, lvmoiscsi, lvmohba ] AND EITHER (i) we've not "upgraded"; OR (ii) we've requested a "raw" volume
* SM backend is an Equalogic in "thick" mode
* SM backend is of type CSLG

Clearly this logic is in the wrong place...

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@eu.citrix.com>
Acked-by: Jonathan Ludlam <e7e3380887a8f95cc9dc4f0d51dedc7e849a287a@eu.citrix.com>

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