CA-118425/SCTX-1559: Remove interfaces from bridge before creating VLAN on it

This avoids problems in case the bridge already existed for some reason, e.g.
because it was not cleaned up due to an earlier error condition.

Signed-off-by: Rob Hoes <rob.hoes@citrix.com>
Merge pull request #29 from robhoes/doublevlan

 CA-118425/SCTX-1559: Remove interfaces from bridge before creating VLAN...