SSP-756 Fix demo data date formatting and UUID casting for SQLServer

Early alert closure dates were in a string format SQLServer can't deal
with. Fixed bad values inline in demo_data.xml and also fixed the
groovy script that originally generated them. The original values specified
a MST time, and that field originally carried a timezone in Postgres. But
you're now usually running these demo data scripts *after* everything's
been converted to UTC. So I went ahead and set the time component 7hrs
ahead.

The fix-up scripts in demo_data_1.xml were also broken in SQLServer b/c
casting a UUID to a varchar without specifying a width for the latter
overflows its default size.

You'll need to clear databasechangelog.md5sum for two changesets if you've
already run them:

  update databasechangelog set md5sum = null
  where id in ('Adding Demo Data Set',
    'Fix demo data- person.school_id references');