Add error message for feature not found

Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

configure

@@ -740,6 +740,16 @@ if test -z "$target_list" ; then
     exit 1
 fi
 
+feature_not_found() {
+  feature=$1
+
+  echo "ERROR"
+  echo "ERROR: User requested feature $feature"
+  echo "ERROR: configure was not able to found it"
+  echo "ERROR"
+  exit 1;
+}
+
 if test -z "$cross_prefix" ; then
 
 # ---