Pass check_ip and not hostname.ip to _ComputeNics

This should be done because in the case of --no-name-check there
is no 'hostname.ip' attribute, causing an execution error.
'check_ip' is always set (in CheckArguments) even if --no-name-check
is passed in the command line.

Signed-off-by: Constantinos Venetsanopoulos <cven@grnet.gr>
Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>