title: Make the InputAdornment of an Input unfocusable in Material-UI v1
body: <p>In Material-UI v1 I'm trying to avoid that if a user presses the Tab key while typing in an Input with an InputAdornment, the latter is focused. Instead, what I'm trying to achieve is that by pressing tab the subsequent Input is selected.</p>
  
  <p>It was suggested to me to set the tabIndex property to -1 to avoid it being selected by tabbing but it doesn't appear to work.</p>
  
  <pre><code>&lt;Input
      value={this.state.email}
      endAdornment={
          this.state.email ? (
              &lt;InputAdornment position="end"&gt;
                  &lt;IconButton style={{ width: "32px", height: "32px", tabIndex: "-1" }}&gt;
                      &lt;Icon&gt;clear&lt;/Icon&gt;
                  &lt;/IconButton&gt;
              &lt;/InputAdornment&gt;
          ) : null
      }
  /&gt;
  </code></pre>