Should always return an array

I thought search would return an empty array.  Apparently it it
is not, and not a bad thing to make sure that it always does.
  http://paste.openstack.org/show/40125/

Change-Id: Ia39a092ffae69f94619ac9c640c1ffcc4d70510f

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 This file is used to list changes made in each version of cookbook-openstack-common.
 
+## 0.3.4:
+* Allow `#search_for` to always returns an array.
+
 ## 0.3.3:
 * Incorrectly mocked search results, as a result `#search_for` was performing unnecessary
   actions to an array.

libraries/search.rb

@@ -25,7 +25,8 @@ module ::Openstack
   def search_for role, &block
     query = "chef_environment:#{node.chef_environment} AND roles:#{role}"
 
-    search(:node, query, &block)
+    resp = search(:node, query, &block)
+    resp ? resp : []
   end
 
   # Returns the value for ["openstack"]["memcached_servers"] when

spec/search_spec.rb

@@ -33,6 +33,16 @@ describe ::Openstack do
 
       expect(resp).to eq []
     end
+
+    it "always returns empty results" do
+      @subject.stub(:node).and_return @chef_run.node
+      @subject.stub(:search).
+        with(:node, "chef_environment:_default AND roles:empty-role").
+        and_return nil
+      resp = @subject.search_for("empty-role")
+
+      expect(resp).to eq []
+    end
   end
 
   describe "#memcached_servers" do