allow using assets from global path instead of relative path in tests about handlebars_assets

[pravi]

A crude method is like this, let me try to make it more generic.

--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -80,7 +80,7 @@
       @source = nil
       @patch_path = nil
       @path = nil
-      @assets_path = nil
+      @assets_path = Pathname.new('/usr/share/rubygems-integration/all/gems/handlebars_assets-0.23.2/vendor/assets/javascripts')
     end
 
   end

[pravi]

This change makes all tests except one to pass

--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -80,7 +80,7 @@
       @source = nil
       @patch_path = nil
       @path = nil
-      @assets_path = nil
+      @assets_path = Pathname.new(HandlebarsAssets::PATH)
     end
 
   end

 1) Failure:
HandlebarsAssets::CompilingTest#test_custom_handlebars [/<<PKGBUILDDIR>>/test/handlebars_assets/compiling_test.rb:17]:
Expected /PRECOMPILE CALLED/ to match "{\"compiler\":[7,\">= 4.0.0\"],\"main\":function(container,depth0,helpers,partials,data) {\n    var helper;\n\n  return \"This is \"\n    + container.escapeExpression(((helper = (helper = helpers.handlebars || (depth0 != null ? depth0.handlebars : depth0)) != null ? helper : helpers.helperMissing),(typeof helper === \"function\" ? helper.call(depth0 != null ? depth0 : (container.nullContext || {}),{\"name\":\"handlebars\",\"hash\":{},\"data\":data}) : helper)));\n},\"useData\":true}".

28 runs, 50 assertions, 1 failures, 0 errors, 0 skips

[pravi]

Actually this patch also failed the same way in autopkgtest (the earlier test run was during build). For now I have disabled autopkgtest, but it'd be nice to be able to run it.