[PATCH] only use a slave interface if it has a MAC address defined

[Parsons, Aron]

This patch alters the pre_install_network_config snippet to only use slave interfaces that have a MAC address defined.  Otherwise, if it picks a slave interface without a MAC, /tmp/pre_install_network_config is not generated because the grep statement for the MAC is empty.  This then causes Anaconda to error out because the included file is missing.

/aron