Support volume_readonly_update using XML format

Almost all API support JSON and XML format together,
But this API does not support xml format.
In the request of xml format,
the type of parameter "readonly" in the body is string.
In the request of JSON format,
the type of parameter "readonly" in the body is bool.
But the code only support bool, not support string.
This branch is to solve this problem.

Closes-bug #1244848

Change-Id: I7f2b09a0063df9daad3fdd09789f8e19c43b0aa3
Merge "Support volume_readonly_update using XML format"