This is a sanity check to ensure the footer timestamps on a VHD are
reasonable (e.g. not in the future). This condition can occur if the
local time for the source and destination machines in a migration are
not in agreement, requiring an adjustment to /etc/localtime and/or NTP
reconfiguration.
Without this check there is a risk of importing a corrupt VHD into the
SR causing the entire SR to become corrupted.
Change-Id: I17228e50d6f54632f3bfc32a682e511f876517ec
dd54a15a7f