qemu-img: Use only string options in img_open_opts

img_open_opts() takes a QemuOpts and converts them to a QDict, so all
values therein are strings.  Then it may try to call qdict_get_bool(),
however, which will fail with a segmentation fault every time:

$ ./qemu-img info -U --image-opts \
    driver=file,filename=/dev/null,force-share=off
[1]    27869 segmentation fault (core dumped)  ./qemu-img info -U
--image-opts driver=file,filename=/dev/null,force-share=off

Fix this by using qdict_get_str() and comparing the value as a string.
Also, when adding a force-share value to the QDict, add it as a string
so it fits the rest of the dict.

Cc: qemu-stable@nongnu.org
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Message-id: 20180502202051.15493-3-mreitz@redhat.com
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NMax Reitz <mreitz@redhat.com>
(cherry picked from commit 4615f878)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qemu-img.c

@@ -276,12 +276,12 @@ static BlockBackend *img_open_opts(const char *optstr,
     options = qemu_opts_to_qdict(opts, NULL);
     if (force_share) {
         if (qdict_haskey(options, BDRV_OPT_FORCE_SHARE)
-            && !qdict_get_bool(options, BDRV_OPT_FORCE_SHARE)) {
+            && strcmp(qdict_get_str(options, BDRV_OPT_FORCE_SHARE), "on")) {
             error_report("--force-share/-U conflicts with image options");
             QDECREF(options);
             return NULL;
         }
-        qdict_put_bool(options, BDRV_OPT_FORCE_SHARE, true);
+        qdict_put_str(options, BDRV_OPT_FORCE_SHARE, "on");
     }
     blk = blk_new_open(NULL, NULL, options, flags, &local_err);
     if (!blk) {