Use name as device ID for BIOS RAID arrays (#2335009)

These are treated as disks so we should use just the name, the
same way we do for disks. The names of the BIOS arrays are unique
enought to hopefuly not cause any issues.

blivet/devices/md.py

@@ -793,6 +793,10 @@ def size(self):
         # when teared down.
         return self._size
 
+    @property
+    def device_id(self):
+        return self.name
+
     @property
     def description(self):
         levelstr = self.level.nick if self.level.nick else self.level.name