vm.install-debian: escape commas when passing image path to qemu

slapos/recipe/vm.py

@@ -108,7 +108,8 @@ class BaseRecipe(EnvironMixin):
 
   def getQemuBasicArgs(self, dist, mem=None, snapshot=False,
                              unsafe=False, ssh=None):
-    drive = 'file=%s/%s.img,format=raw,discard=on' % (self.vm, dist)
+    drive = 'file=%s.img,format=raw,discard=on' \
+      % join(self.vm, dist).replace(',', ',,')
     if snapshot:
       drive += ',snapshot=on'
     elif unsafe: