Recently e1000 NIC support was added to bhyve; implement that in
the bhyve driver:
- Add capability check by analyzing output of the 'bhyve -s 0,e1000'
command
- Modify bhyveBuildNetArgStr() to support e1000 and also pass
virConnectPtr so it could call bhyveDriverGetCaps() to check if this
NIC is supported
- Modify command parsing code to add support for e1000 and adjust tests
- Add net-e1000 test
