g2testvm: Use rhel7 for os-variant

The `fedora23` OS variant has been removed. Since Fedora moves fairly
quickly, using `rhel7` is more robust anyway.

g2testvm.sh

@@ -73,7 +73,7 @@ virt-install \
 	--vcpus 2 \
 	--cpu host \
 	--import \
-	--os-variant fedora23 \
+	--os-variant rhel7 \
 	--boot kernel=${KERNEL},initrd=${INITRD},kernel_args=${KCMDLINE} \
 	--disk vol=${POOL}/${name}.qcow2 \
 	--network bridge=${BRIDGE},model=virtio \