block: add block driver read only whitelist

We may want to include a driver in the whitelist for read only tasks
such as diagnosing or exporting guest data (with libguestfs as a good
example). This patch introduces a readonly whitelist option, and for
backward compatibility, the old configure option --block-drv-whitelist
is now an alias to rw whitelist.

Drivers in readonly list is only permitted to open file readonly, and
returns -ENOTSUP for RW opening.

E.g. To include vmdk readonly, and others read+write:
    ./configure --target-list=x86_64-softmmu \
                --block-drv-rw-whitelist=qcow2,raw,file,qed \
                --block-drv-ro-whitelist=vmdk

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

scripts/create_config

@@ -34,8 +34,15 @@ case $line in
     done
     echo ""
     ;;
- CONFIG_BDRV_WHITELIST=*)
-    echo "#define CONFIG_BDRV_WHITELIST \\"
+ CONFIG_BDRV_RW_WHITELIST=*)
+    echo "#define CONFIG_BDRV_RW_WHITELIST\\"
+    for drv in ${line#*=}; do
+      echo "    \"${drv}\",\\"
+    done
+    echo "    NULL"
+    ;;
+ CONFIG_BDRV_RO_WHITELIST=*)
+    echo "#define CONFIG_BDRV_RO_WHITELIST\\"
     for drv in ${line#*=}; do
       echo "    \"${drv}\",\\"
     done