This converts a great many configuration options to the new
standard format.

Fixes a segfault seen in the wild with providers=files

This reverts commit 8c50bd085c0efe5fde354deee2c8118887aae29d.

Amended: commit 1016af2b1b97ad4290ccce8fa462cc7e3c191b2e also made
use of the SYSLOG_ERROR() macro, so those portions of that code
also needed to be reverted.

This is just a band-aid until ELAPI is fully functional and ready to
use.

There was a chance that groups w/o members could end up causing a failure to
store the group. This would happen in case the structure used by glibc to fill
up the group data was "dirty". Always memset structures before passing them to
te libc and also check if there are any members, before calling the async
function.
Finally add some tracing at level 7 so that it is easier to follow what is going
on in case of touble.

Add helpers functions to query/set the offline status per backend.
Now all providers share the same offline status.

The code was still dependent on it for the ldap driver.
Changed the driver code to depend on the schema type.
Fix defaults for user and groups trees.
ATM if you use the rfc2307bis schema you have to put users and groups
in 2 separate trees (what people does by default anyway.
If this limitation will turn to be too hard, we will change this later.

New tevent library finally outlawed nested loops.