[FIX] web,survey: update graphs tooltip to new nvd3

with the update of nvd3/d3, the tooltip api was changed.  This commit
updates the 3 last places where we were using the tooltips.

addons/survey/static/src/js/survey_result.js

@@ -50,12 +50,14 @@ if(!$('.js_surveyresult').length) {
 
     //initialize discreteBar Chart
     function init_bar_chart(){
-        return nv.models.discreteBarChart()
+        var chart = nv.models.discreteBarChart()
             .x(function(d) { return d.text; })
             .y(function(d) { return d.count; })
             .staggerLabels(true)
-            .tooltips(false)
             .showValues(true);
+
+        chart.tooltip.enabled(false);
+        return chart;
     }
 
     //initialize Pie Chart

addons/web/static/src/js/views/form_widgets.js

@@ -738,9 +738,10 @@ var FieldPercentPie = common.AbstractField.extend({
                 .donut(true) 
                 .showLegend(false)
                 .showLabels(false)
-                .tooltips(false)
                 .color(['#7C7BAD','#DDD'])
                 .donutRatio(0.62);
+
+            chart.tooltip.enabled(false);
    
             d3.select(svg)
                 .datum([{'x': 'value', 'y': value}, {'x': 'complement', 'y': 100 - value}])
@@ -778,12 +779,13 @@ var FieldBarChart = common.AbstractField.extend({
                 .width(width)
                 .height(height)
                 .margin({top: 0, right: 0, bottom: 0, left: 0})
-                .tooltips(false)
                 .showValues(false)
                 .transition(350)
                 .showXAxis(false)
                 .showYAxis(false);
-   
+
+            chart.tooltip.enabled(false);
+
             d3.select(svg)
                 .datum([{key: 'values', values: value}])
                 .transition()