Add dit recipe.

This recipe allows to create the DIT based on a definition provided by the
'cg_openldap/dit.json' data bag item, it if exists, or the node attribute
'node.cg_openldap.dit' otherwise.

Therefore the DIT is no longer created by the server recipe.
Add configuration of the log level.

The log level of the main BDB database is configured by the server
recipe according to the cg_openldap.server_log_level node attribute.
Refactor the populate recipe.

This recipe populates the directory with respect to the
cg_openldap/populate.json data bag item.

This commit also include refactoring of low level methods, therefore
other recipes have been updated accordingly.