LdapImpl.java: Add new method for user creation.

The new method will have to be refactored to increase
code reusability.
Add integration test for new LdapImpl method.
LdapImpl.java: Refactor createUserFromLdap().

The method doing the actual user query and creation
has been extended with a boolean parameter controlling the
password check code path. This allows the username-only
method to delegate to the original method.
LdapImpl.java: General code and comment cleanup.
Fix tests: use new password check flag.
Update LDAP password providers with new flag.