Allow newer versions of Flask
Allow newer versions of Flask

Since keystone bumped the version of Flask in openstack/requirements,
the upper constraint is now equal to 1.0.2 that is not allowed by
the requirements.txt of designate.

If we change the designate requirements, we could use the same
version of Flask for both Keystone and Designate, helping
deployers.

Change-Id: Ic54ceebc1af5a9d74e415f7369e1d5bb19c6e915

openstack/designate,openstack/designate,openstack/designate