[WIP] Cisco support for Neutron configuration

*First patch*
Bring n1kv_vem driver support to vSwitch configuration in Neutron
Compute & Network agent.
It use the n1kv_vem agent from puppet-neutron using default parameters
that could be replaced by custom datas.
Also add an unit test with a new context when running n1kv_vem agent.

*Second Patch*
WIP