[ha] Fix tenant NIC OS config for VLAN ranges

[ha] Fix tenant NIC OS config for VLAN ranges

Previous commits added support for tenant VLAN range parametrization,
yet failed to accomodate the new VLAN range representation ('M:N') in
existing `linux.network.interfaces` reclass configuration.

This lead to the silent removal of <nic_private>.<vlan_private> from
interfaces file and for `br-mesh` to try to use <nic_private> instead
of <nic_private>.<vlan_private>, conflicting with `br-floating`.

Stick to using the first VLAN in the tenant range.

JIRA: FUEL-365

Change-Id: I88f7263159f1742dba3b6e36649c9344f2932c5f
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>