Wrong timestamp in file

[mkuhring]

https://github.com/42on/ceph-collect/blob/master/ceph-collect#L34

DATETIME_FORMAT="%Y%m%d_%H%I%S" produces a 24-hours, 12-hours, seconds suffix.

I guess is supposed to be 24-hours, minutes, seconds.
So %H%M%S.

I just noticed it when testing the script, generating several tarballs which were missorted.
Actually went checking if time is out of sync on our ceph hosts and docker container.
Before noticing the "cosmetic" bug in the script.