qemu.tests: Add a test case for test invalid parameters in nic device

This case is designed to test the qemu behavior when it get invcalid parameters.
Qemu should quit with some warning message but not core dump.

Signed-off-by: Yiqiao Pu <ypu@redhat.com>
Merge pull request #66 from ypu/invalid_parameter

qemu.tests: Add a test case for test invalid parameters in nic device