Delete test_create_vnffg_pre() for Python3 unittest
Delete test_create_vnffg_pre() for Python3 unittest

In Python3 test, the test "test_create_vnffg_pre()" affects
other tests regarding mocked "__new__" part.
Because most part of this test are covered in
test_create_vnffg_abstract_types(), this test should be deleted.

Change-Id: Icf118cbb3e9dda745248cedbe16a6d4a0be1569f

stackforge/tacker,openstack/tacker,openstack/tacker,stackforge/tacker,openstack/tacker