Fix ldap admin-value parsing to allow spaces in binding strings
Fix ldap admin-value parsing to allow spaces in binding strings

The `aslist` function has default `flatten=True`
(https://docs.pylonsproject.org/projects/pyramid/en/latest/api/settings.html) which will make ldap
binding strings with spaces unusable.
The `flatten` flag will cut the binding strings and you won't be able to
match `admin_value` list against the `admin_field` values.

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