Remove LDAP password hashing code

Keystone should not be hashing passwords for LDAP users
itself.  Password hashing should be performed by the LDAP
server, as password policies may not allow pre-hashed
passwords to be set (they may enforce a scheme that is
stronger that salted SHA-1).

This removes the LDAP password hashing code.  When using
fakeldap for running unit tests, passwords will not be
hashed.  For this reason, the hashing tests are skipped
for LDAP backends.

Closes-bug: 1308793
Change-Id: Ia0998b7fd8fb5d01b86a947d18b7e79fcffd1228
Merge "Remove LDAP password hashing code"