stackdriver: make it possible to use alignment period template variable

public/app/plugins/datasource/stackdriver/partials/query.aggregation.html

@@ -22,8 +22,6 @@
     <div class="gf-form-select-wrapper gf-form-select-wrapper--caret-indent">
       <gf-form-dropdown model="ctrl.target.aggregation.perSeriesAligner" get-options="ctrl.alignOptions" class="gf-form width-12"
         disabled type="text" allow-custom="true" lookup-text="true" css-class="min-width-12" on-change="refresh()"></gf-form-dropdown>
-      <!-- <select class="gf-form-input width-14" ng-model="ctrl.target.aggregation.perSeriesAligner" ng-options="f.value as f.text for f in ctrl.alignOptions"
-        ng-change="refresh()"></select> -->
     </div>
 
     <div class="gf-form gf-form--grow">
@@ -35,8 +33,8 @@
   <div class="gf-form">
     <label class="gf-form-label query-keyword width-9">Alignment Period</label>
     <div class="gf-form-select-wrapper gf-form-select-wrapper--caret-indent">
-      <select class="gf-form-input width-12" ng-model="ctrl.target.aggregation.alignmentPeriod" ng-options="f.value as f.text for f in ctrl.alignmentPeriods"
-        ng-change="refresh()"></select>
+      <gf-form-dropdown model="ctrl.target.aggregation.alignmentPeriod" get-options="ctrl.alignmentPeriods" class="gf-form width-12"
+        disabled type="text" allow-custom="true" lookup-text="true" css-class="min-width-12" on-change="refresh()"></gf-form-dropdown>
     </div>
   </div>