[Spec] Correctly stub the sources used for search

Before, we was stubbing something which wasn't called and thus searching
the whole master repository. This change shaves 20 seconds off the
testing time.

Gemfile.lock

@@ -7,7 +7,7 @@ GIT
 
 GIT
   remote: https://github.com/CocoaPods/Core.git
-  revision: 6150528fee42ddfe5eb83ed21741f718da027792
+  revision: f7406aa52c9a60943af7d2365ff0c2095bbb46ec
   branch: master
   specs:
     cocoapods-core (0.34.2)

spec/functional/command/search_spec.rb

@@ -7,7 +7,7 @@ module Pod
 
     before do
       @test_source = Source.new(fixture('spec-repos/test_repo'))
-      SourcesManager.stubs(:all).returns([@test_source])
+      Source::Aggregate.any_instance.stubs(:sources).returns([@test_source])
       SourcesManager.updated_search_index = nil
     end
 
@@ -40,7 +40,7 @@ module Pod
       output.should.not.include? 'BananaLib'
     end
 
-    it 'restricts the search to Pods supported on iOS' do
+    it 'restricts the search to Pods supported on OS X' do
       output = run_command('search', 'BananaLib', '--osx')
       output.should.not.include? 'BananaLib'
     end