Pass the baremetal bridge to create-nodes

devtest_testenv gained support for OVS bridges and test
environment numbers in 18a43f6db3e29837a5986fff488c2f4e4cd42034,
however that patch did not pass the baremetal bridge to create-nodes,
which means created nodes would not be added to it.

Change-Id: Ifd3ade24246608dcd68627a78c05c78661db2b17