compare s3's last modified time using server's timezone

S3's last modified time is stored in utc timezone,
but displayed in server's timezone.
Prior to this fix, no timezone calculation was made,
so test_ls_command.py kept failing for some timezones.

In my case, I'm living in UTC+9. UTC time "2014-01-09T20:45:49" is "2014-01-10 05:45:49" in my local time.
but regex pattern is "2014-01-09 \\d{2}:\\d{2}:\\d{2}".
As you see date is different, so this test kept failing in my local machine.

This fix tests displayed last modified time using server's timezone.