pytests: sid_strings: do not fail if epoch ending has zeros

pytests: sid_strings: do not fail if epoch ending has zeros

To avoid collisions in random OID strings, we started using the epoch
date modulus 100 million. The trouble is we did not strip out the
leading zeros, so the field might be '00000123' when it should be
'123', if the date happened not to correspond to an epoch with a zero
in the eighth to last place. This has been the case for most of the
last 1041 days, but fortunately the bug was only introduced earlier
this year.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15520

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Martin Schwenke <mschwenke@ddn.com>