Bring it out of sysdb, which will slowly remove internal dependencies on
domains and instead will always require them to be passed by callers.

Removing bad examples of usage of sysdb_transaction_start/commit/end
functions and making it more consistent (all files except of
src/db/sysdb_*.c).

The patch also updates code using modified functions. Tests have also
been adjusted.

https://fedorahosted.org/sssd/ticket/930

Since the sysdb is now synchronous and creates its own event context we
don't need an explicit event context anymore in the tools.

This commit completes the migration to a synchronous sysdb