Fix the bug about nic conflict
Fix the bug about nic conflict

If guest_networks include multiple networks, and some of them set nic but some not,
the current code would result to nic conflict

Change-Id: I2207c46427de6e1a26e5887dc436c41342034d9c

mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk,mfcloud/python-zvm-sdk