s4: Major rework of the LDB/SAMDB/IDMAP python bindings

s4: Major rework of the LDB/SAMDB/IDMAP python bindings

- Centralise the lookups for the default domain (root) in the call "domain_dn"
- Reduce the LDB connections attempts ("connect" calls) from three to one
  - tools should load faster
- Make the LDB connection init more like the "ldb_wrap_connection" call
- Load the right UTF8 casefolder which fixes up problems with special characters
  (discovered by me: e.g. small "Umlaute" (ä, ö, ü, ...) in the DN weren't upcased
  - so records "seemed" lost in TDB)