Fix LDAP Identity with non-zero user_enabled_default

The LDAP Identity backend was not properly using the
user_enabled_default option as a string. This caused
operations to fail with

 TypeError: unsupported operand type(s) for &: 'str' and 'int'

Partial-Bug: #1210175

Change-Id: I54931e669186871d18dea088870945b9de40d573
Fix LDAP Identity get user with user_enabled_mask

Fetching users using the LDAP Identity backend would fail with

 KeyError: 'enabled'

from _ldap_res_to_model when user_enabled_mask is not 0.

Change-Id: I39a9606ba7210f0fea064abd6adad379218b432b
Closes-Bug: #1210175