Set correct linux distro for packer

The current packer variables list centos-7 instead of centos as the
configuration file name. Therefore the build matrix needs to be updated

Change-Id: I5e4ee8973bbf3f3f70f6ab1670f5c2620b69d23f
Signed-off-by: Andrew Grimberg <agrimberg@linuxfoundation.org>
1 file changed