CA-78901: Fix snapshot info for SXM'ed snapshot disks

Once we have copied all snapshot disks to the remote SR and mirrors are
running for all live VDIs, rebuild the snapshot tree on the remote SR
for each live VDI.

Signed-off-by: John Else <john.else@citrix.com>
Ignore Unknown_RPC exceptions in update_snapshot_info

Signed-off-by: John Else <john.else@citrix.com>