title: Custom initializer for get_variable
body: <p>How can one specify a custom initializer as the third argument for <code>tf.get_variable()</code>? Specifically, I have a variable <code>y</code> which I want to initialize using another (already initialized) variable <code>x</code>. </p>
  
  <p>This is easy to do using <code>tf.Variable()</code>, just say, <code>y = tf.Variable(x.initialized_value())</code>. But I couldn't find an analog in the documentation for <code>tf.get_variable()</code>.</p>