Rename vsphere-xcopy-volume-populator image to vsphere-copy-offload-populator

This evolving feature created 2 more ways to speed-up the content copy, which are not XCOPY specific:
1. Fallback, aka host-copy:
The tool vmkfstools sending the XCOPY command, handles internally a failure from the server, if something is misconfigured
like paths and networks, or even if the support for XCOPY is disable or rejected by the storage array. In that case it
falls back to performing i/o reads and i/o writes on the ESX itself. This still results a faster copy times than VDDK
mostly because the ESX is connected to faster, and less congested storage networks. For Dell PowerFlex which doesn't
even support XCOPY to begin with this is always the case.
2. vVols and Volume-copy API:
vVols disks are volumes on the array, and some arrays have an API call to copy a source volume onto an existing one.
We take advantage of that and call that API on the target volume we create using the CSI and the result is near instant
copy times, without involvement of the ESX,vmkfstoosl or any other bits from the regular XCOPY flow.

It is plausible then to create a more comprehensive name that will clearly convey the feature behavior without confusion.