[brightbox|compute] Updates to Test helper for select image

* Extracted Image API lookup
* Removed inline rescue

tests/brightbox/requests/compute/helper.rb

@@ -42,13 +42,20 @@ class Brightbox
     module TestSupport
       # Find a suitable image for testing with
       # For speed of server building we're using an empty image
+      #
+      # Unless the tester has credentials this will fail so we rescue
+      # any errors and return nil.
+      #
+      # This is used in the shared file +tests/compute/helper.rb+ so unfortunately
+      # makes all tests reliant on hardcoded values and each other
+      #
+      # @return [String,NilClass] the most suitable test image's identifier or nil
       def self.image_id
         return @image_id unless @image_id.nil?
-        images = Fog::Compute[:brightbox].list_images
-        raise "No available images!" if images.empty?
-        image = images.select {|img| img.size == 0 }.first
-        image = images.first if image.nil?
+        image = select_testing_image_from_api
         @image_id = image["id"]
+      rescue
+        @image_id = nil
       end
 
       # Prepare a test server, wait for it to be usable but raise if it fails
@@ -62,6 +69,13 @@ class Brightbox
         server
       end
 
+    private
+      def self.select_testing_image_from_api
+        images = Fog::Compute[:brightbox].list_images
+        raise "No available images!" if images.empty?
+        images.select {|img| img.size == 0 }.first || images.first
+      end
+
     end
     module Formats
       module Struct

tests/compute/helper.rb

@@ -15,7 +15,7 @@ def compute_providers
     },
     :brightbox  => {
       :server_attributes => {
-        :image_id => (Brightbox::Compute::TestSupport.image_id rescue 'img-wwgbb') # Ubuntu Lucid 10.04 server (i686)
+        :image_id => Brightbox::Compute::TestSupport.image_id
       },
       :mocked => false
     },