SlapObject: Fix supervisord config generation

Previous code matched way too many files as belonging to the current
partition and wrongly removed them as obsolete: e.g. when processing
slappart1, all the configuration files belonging to slappart10 would
systematically be deleted, as if they belonged to slappart1 and were
now out-of-date. Same for all partitions starting with 'slappart1',
such as slappart11, slappart12, etc.

This resulted in all services in slappart1X being stopped and started
repeatedly and very often: stopped during processing of slappart1 and
started during processing of slappart1X, with potentially several
minutes of downtime, and a high percentage of downtime.

This is a fixup of db98a521.