scripts/qom-fuse: ensure QOMFuse.read always returns bytes

- Use FuseOSError to signal ENOENT instead of returning it
- Wrap qom-get in str(), as we don't always know its type
- The empty return should be b'', not ''.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210603003719.1321369-15-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

scripts/qmp/qom-fuse

@@ -127,19 +127,19 @@ class QOMFuse(QOMCommand, Operations):
 
     def read(self, path, size, offset, fh):
         if not self.is_property(path):
-            return -ENOENT
+            raise FuseOSError(ENOENT)
 
         path, prop = path.rsplit('/', 1)
         if path == '':
             path = '/'
         try:
-            data = self.qmp.command('qom-get', path=path, property=prop)
+            data = str(self.qmp.command('qom-get', path=path, property=prop))
             data += '\n'  # make values shell friendly
         except QMPResponseError as err:
             raise FuseOSError(EPERM) from err
 
         if offset > len(data):
-            return ''
+            return b''
 
         return bytes(data[offset:][:size], encoding='utf-8')