HFX-1192: Clearwater SP1 hotfix: xapi fix for Time zone reset during VM ...

...migrations from pre-6.1 XS during RPU

merge from CA-128803: do not take timeoffset from last boot record for HFX-1192
This is specially for upgrades from pre-xenopsd XenServers.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>