Convert blob_key_generator_spec to lightweight_spec_helper (Phase 1 - Batch 4)

Batch 4 Results:
- Converted 1 file (2 tests)
- Many attempted files had hidden dependencies

File converted:
- blob_key_generator_spec.rb (2 tests)

Cumulative: 11/400 files (2.75%), ~7s savings

Author: johha

spec/unit/lib/cloud_controller/blobstore/blob_key_generator_spec.rb

@@ -1,4 +1,5 @@
-require 'spec_helper'
+require 'lightweight_spec_helper'
+require 'cloud_controller/blobstore/blob_key_generator'
 
 module CloudController
   module Blobstore