Ignore ResourceExists errors from bbs_apps_client

- This is a re-implementation of 133486e
- This error can be raised by BBS when there is a race condition between
  the CC syncer and CC API when creating an LRP for a process
- Since we want to desire a process anyway, it already existing (with
  the correct version) is likely not an error case. Thus, we can behave
  idempotently.
- Improvements from previous implementation:
    - No longer ignores other types of APIErrors in
      desire_app_handler.rb
    - No longer coupled to the exact error message coming from BBS

Author: Gerg

lib/cloud_controller/diego/bbs_apps_client.rb

@@ -16,7 +16,7 @@ def desire_app(process)
           logger.info('desire.app.response', process_guid: lrp.process_guid, error: response.error)
 
           runner_invalid_request!(response.error.message) if response.error&.type == ::Diego::Bbs::ErrorTypes::InvalidRequest
-          return response if response.error&.type == ::Diego::Bbs::ErrorTypes::ResourceConflict
+          return response if [::Diego::Bbs::ErrorTypes::ResourceConflict, ::Diego::Bbs::ErrorTypes::ResourceExists].include?(response.error&.type)
 
           response
         end

spec/unit/lib/cloud_controller/diego/bbs_apps_client_spec.rb

@@ -51,6 +51,14 @@ module VCAP::CloudController::Diego
           end
         end
 
+        context 'when the bbs response contains a resource exists error' do
+          let(:lifecycle_error) { ::Diego::Bbs::Models::Error.new(type: ::Diego::Bbs::Models::Error::Type::ResourceExists) }
+
+          it 'does not raise error' do
+            expect { client.desire_app(process) }.not_to raise_error
+          end
+        end
+
         context 'when the bbs response contains an invalid request error' do
           let(:lifecycle_error) { ::Diego::Bbs::Models::Error.new(type: ::Diego::Bbs::Models::Error::Type::InvalidRequest, message: 'bad request') }