[LNT] Fix the graph page to show multiple metrics for the same test

[kpdev42]

Summary

Note: request.args is a dict and duplicate keys are ignored.
Currently the plot args have the following format plot.unused=m.t.f where unused is the test id.
If you select few metrics for the same test (for example compile_time and execution_time) on the Run page and click Graph,
the URL will look like /db_default/v4/nts/graph?plot.958=5.958.2&plot.958=5.958.3
The second plot argument with the same key will be ignored. This patch fixes this issue.

OS Laboratory. Huawei Russian Research Institute. Saint-Petersburg

[cmatthews]

LGTM. Thanks!

lnt/server/ui/templates/v4_run.html

<form id="graph_selection_form" method="GET" action="{{ graph_base }}">
             {% if options.show_mad %}<th>MAD</th>{% endif %}
             {% if options.show_all_samples %}<th>Samples</th>{% endif %}
             {% if options.show_sample_counts %}<th>N</th>{% endif %}
           </tr>
         </thead>
         <tbody class="searchable">
           {% for test_name,test_id,cr in tests %}
             <tr>
-              <td><input type="checkbox" name="plot.{{test_id}}" value="{{machine.id}}.{{test_id}}.{{field_index}}"/></td>
+              <td><input type="checkbox" name="plot.{{test_id}}.{{field_index}}" value="{{machine.id}}.{{test_id}}.{{field_index}}"/></td>
               <td class="benchmark-name">
                 <a href="{{graph_base}}&amp;plot.{{test_id}}={{ machine.id}}.{{test_id}}.{{field_index}}">
                   {{ test_name }}
                 </a>
                 {{ utils.render_profile_link(cr.cur_profile, cr.prev_profile, run.id, compare_to.id, test_id) }}
               </td>
               {{ get_cell_value(cr, field) }}
             </tr>