use logfile feature of OpenLDAP 2.6

[davidcoutadeur]

it would be useful to have the logfile feature in:

• the config templates
• the buildconfigtemplate action

[davidcoutadeur]

done in e001b47 + 8d78c11

TODO:

• re-enable logfile-rotate parameter https://bugs.openldap.org/show_bug.cgi?id=9730 is fixed

• find a way to make logs work for both standard logging in logfile, and output of the debug action of slapd-cli

  Note: standard logging happens only when adding the logfile-only directive. Output of the debug action only occurs when logfile-only is absent.

[davidcoutadeur]

logfile-rotate is re-enabled and updated in commit 317a8c4

[davidcoutadeur]

Everything seems ok for 2.9 release