Merge pull request #161 from ypu/nic_promisc

generic.tests: Update the cfg for nic_promisc to support Windows guest

generic/tests/cfg/nic_promisc.cfg

 - nic_promisc: install setup image_copy unattended_install.cdrom
     virt_test_type = qemu libvirt
-    only Linux
     type = nic_promisc
     filesize = 400
     transfer_timeout = 100
     transfer_type = remote
+    Windows:
+        clean_cmd = erase