Can't skip constraint validation if the value is None

[huangtianhua]

The code as bellow, if the value is None, the constraint validation won't do:
def get_value(self, value, validate=False):
......
# property value resolves to None if resource it depends on is not
        # created. So, if value is None skip constraint validation.
        if value is not None and validate:
            self.schema.validate_constraints(_value, self.context)
......

The bug/1339942 has been merged, and it fixes checks reference on another
resource and skips validation if resource is in INIT state.
So if there is no dependency, we need to do the constraint validation of None value.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/174728

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/174728
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=4f0a8883167ecc03fbe74d5a72f3b2edc5c137a9
Submitter: Jenkins
Branch: master

commit 4f0a8883167ecc03fbe74d5a72f3b2edc5c137a9
Author: huangtianhua <email address hidden>
Date: Fri Apr 17 14:56:02 2015 +0800

    Do constraint validation for None value property

    Should do constraint validation for None value property
    when validate if the property has no dependency of any other
    Init resource.

    Change-Id: Ie22d01de517f25b1f160c84c8c94b8950e528399
    Closes-Bug: #1444898