xci: roles: configure-network: Avoid passing empty string to module

xci: roles: configure-network: Avoid passing empty string to module

The package module gets upset if we pass it an empty string as a package
name

Mar 09 15:15:33 TASK [configure-network : Ensure networking packages are present] **************
Mar 09 15:15:49 fatal: [opnfv]: FAILED! => {"changed": false, "failed":
true, "msg": "No package matching '' found available, installed or
updated", "rc": 126, "results": ["iproute-3.10.0-87.el7.x86_64 providing
iproute is already installed", "No package matching '' found available,
installed or updated"]}

As such, lets pass an existing package for non-Debian distros to make
the module happy.

Change-Id: Ib1128057097193278cfe50f79daf35332b54e781
Signed-off-by: Markos Chandras <mchandras@suse.de>