Use UTC when expiring slices.
Use UTC when expiring slices.

Fix a bug with slice expiration where localtime was used to look for
expired slices, causing slice expiration to be off by the number of
hours from UTC.

charliemeyer/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal