Fix timezone in framework_pg renew_slice.
Fix timezone in framework_pg renew_slice.

The timezone was dropped by the strftime call. Use isoformat instead
to keep the timezone.

GENI-NSF/gram,plantigrade/geni-tools,tcmitchell/geni-tools,ahelsing/geni-tools,plantigrade/geni-tools,tcmitchell/geni-tools,ahelsing/geni-tools,GENI-NSF/gram,GENI-NSF/gram