configure: display "no" for disabled kvm/vhost-net

Fix configure display for non-Linux OS's and the KVM /
vhost-net features to show "no" output instead of nothing
at the end of the line.

Signed-off-by: Brad Smith <brad@comstyle.com>
Acked-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

configure

@@ -113,7 +113,6 @@ curl=""
 curses=""
 docs=""
 fdt=""
-kvm=""
 nptl=""
 sdl=""
 vnc="yes"
@@ -129,9 +128,10 @@ xen=""
 xen_ctrl_version=""
 linux_aio=""
 attr=""
-vhost_net=""
 xfs=""
 
+vhost_net="no"
+kvm="no"
 gprof="no"
 debug_tcg="no"
 debug_mon="no"