Remove duplicated assertion

"assert_domain_enabled" method is called within "assert_user_enabled", no need perform duplicated assertion

Change-Id: I4a7895bbda614bbf31b3d3c1805389aa4465b2fb
Signed-off-by: Dave Chen <wei.d.chen@intel.com>
Convert unicode to UTF8 when calling ldap.str2dn()

The string passed to ldap.str2dn() needs to be UTF8 encoded, otherwise
we encounter UnicodeEncodeError exceptions.

This patch adds UTF8 encoding where it was missing for ldap.str2dn()
calls as well as some unit tests to cover the functions that were
lacking this encoding step.

Change-Id: I96e718f1d43f4aad272ca4990d3905a5adf1f07d
Closes-bug: #1375139
Handle default string values when using user_enabled_invert

When the user_enabled_invert setting is being used, values returned
from LDAP are ultimately converted to a bool type when we reach the
inversion logic.  If the user_enabled_default value is used due to
no value being returned from LDAP, the type is a string.  This causes
the inversion logic to be evaluated incorrectly, as 'not' will return
False for any non-empty string.  This results in disabled accounts
that should be enabled.

Change-Id: Id7b024c12815748305458ca05fc8f8a6324c1908
Closes-bug: #1376053
Merge "Convert unicode to UTF8 when calling ldap.str2dn()"
Merge "Handle default string values when using user_enabled_invert"
Merge "Remove duplicated assertion"