reclass: Revert virt.nic to hardcoded eth{0,1}

reclass: Revert virt.nic to hardcoded eth{0,1}

Salt's virtualization model for virt:nic:default does not use real
interface names that are present on the node, but instead it defaults
to using "ethX" notation, that name being only a convention inside
Salt internals.

Moreover, the 'salt.control.virt' reclass class (located in
/srv/salt/reclass/classes/system/salt/control) already provides a
defalt maping between "eth{0,1}" and "br{0,1}". Using anything
different than "eth{0,1}" will lead to 2 extra (broken) mappings.

Reverting the changes in "virt:nic" reclass fixes both the python
exception recently introduced, as well as the broken defaults.

Change-Id: I5c90e3d2bc181c1ad3d87af64440439e6a41fb28
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>