Don't use specific NIC for cisco_coi_user.common

Currently cisco_coi_user.common.yaml assumes that there's an
IP address on eth0.  This will cause an interpolation error
when running the install scripts if there's not an address
actually assigned to the NIC.  A safer default would be
to simply use $ipaddress instead.

Closes-Bug: #1260787
Merge pull request #17 from CiscoSystems/bugs/1260787

Don't use specific NIC for cisco_coi_user.common