[ldap auth] make sure imported passwords from LDAP are encrypted (closes #2583994) When a user is imported from an LDAP source (in ldapfeed or when converting a user from an ldapsource to system one), we may import a clear-text password, which we do not want to do in our system database.

doc/book usr/share/doc/cubicweb-documentation
doc/html usr/share/doc/cubicweb-documentation
debian/cubicweb-doc usr/share/doc-base/cubicweb-doc