Fix instance modal styles

awx/ui/client/src/instance-groups/instances/instance-modal.block.less

@@ -1,3 +1,7 @@
+#instance-modal .at-Panel-headingRow {
+  margin-bottom: @at-space-4x;
+}
+
 .Modal-backdrop {
  background: #000;
  height:100%;

awx/ui/client/src/instance-groups/instances/instance-modal.partial.html

@@ -23,7 +23,8 @@
                     collection="vm.instances"
                     dataset="vm.dataset"
                     search-tags="vm.searchTags"
-                    query-set="vm.querySet">
+                    query-set="vm.querySet"
+                    search-bar-full-width="true">
                 </smart-search>
             </div>
             <at-list results='vm.instances'>