[nailgun] Add vlan_splinters feature

Add 'vlan_splinters' checkbox to the fixture.
Propagate correct set of vlan ids to deployment json.
Add tests.
Fix noseargs propagation in run_tests.sh

Change-Id: I1fbd31b5336894997f7ddf0920974c8f947d9854
Merge "[nailgun] Add vlan_splinters feature" into 3.2-fixes