Reverted use of DateUtils.parseDateStrictly.

- The use of DateUtils.parseDateStrictly was removed in favor of using
  the SimpleDateParser and ParsePosition directly, as the DateUtils'
  function does not exist in the version of the Apache library available
  to RHEL6.
Merge pull request #792 from candlepin/crog/gb-parsedate-fix

Reverted use of DateUtils.parseDateStrictly.