The param 'readonly' is incorrect checked

In the function os-update_readonly_flag, the param 'readonly' is incorrect
checked, without the param in request, i think it should raise exception
with message like "Must specify readonly in request."

Change-Id: I19e15e988ffa2d093d374f6a33ce94d45ffe2c30
Closes-bug: 1254682
Merge "The param 'readonly' is incorrect checked"