Disable restricts of sdnvpn test cases

Disable restricts of sdnvpn test cases

1. The original testcases.yaml file of Functest restricts sdnvpn test cases
   to run on Fuel, Apex or Netvirt on bgpvpn scenario.
https://github.com/opnfv/functest/blob/master/functest/ci/testcases.yaml#L278
2. Dovetail has a testcases.yaml file to allow sdnvpn test cases run on
   any commercial SUTs.
https://github.com/opnfv/dovetail/blob/master/etc/userconfig/testcases.yaml#L113

Change-Id: I0d5ed5b22e55dc3dc0fe584dc57b28239334b7de
Signed-off-by: xudan <xudan16@huawei.com>