test_router_dhcp_opts has been failing on the smoke tests on 4.8 ,4.9, 4.10. This is new test added as part of fix for "
CLOUDSTACK-9598: wrong defaut gateway for the nic in non-default network"
Marvin VirtualMachine object's nic attribute, does not store nics in any particular order. test made the assumption the nic is default nic of the virtual machine which may not necessarily true all the time
nic objects 'isdefault' attribute can be used to verify if the nic is default nic.