Extract and simplify more code into BaseRepositoryService`

`try_to_set_repository_read_only!` is now on the Base class.
Simplified Exception classes from 2 to 1 with a more descriptive name.

app/services/projects/hashed_storage/base_repository_service.rb

@@ -2,11 +2,8 @@
 
 module Projects
   module HashedStorage
-    # Returned when there is an error with the Hashed Storage migration
-    RepositoryMigrationError = Class.new(StandardError)
-
-    # Returned when there is an error with the Hashed Storage rollback
-    RepositoryRollbackError = Class.new(StandardError)
+    # Returned when repository can't be made read-only because there is already a git transfer in progress
+    RepositoryInUseError = Class.new(StandardError)
 
     class BaseRepositoryService < BaseService
       include Gitlab::ShellAdapter
@@ -55,6 +52,16 @@ module Projects
         move_repository(new_disk_path, old_disk_path)
         move_repository("#{new_disk_path}.wiki", old_wiki_disk_path)
       end
+
+      def try_to_set_repository_read_only!
+        # Mitigate any push operation to start during migration
+        unless project.set_repository_read_only!
+          migration_error = "Target repository '#{old_disk_path}' cannot be made read-only as there is a git transfer in progress"
+          logger.error migration_error
+
+          raise RepositoryInUseError, migration_error
+        end
+      end
     end
   end
 end

app/services/projects/hashed_storage/migrate_repository_service.rb

@@ -35,18 +35,6 @@ module Projects
 
         result
       end
-
-      private
-
-      def try_to_set_repository_read_only!
-        # Mitigate any push operation to start during migration
-        unless project.set_repository_read_only!
-          migration_error = "Target repository '#{old_disk_path}' cannot be made read-only as there is a git transfer in progress"
-          logger.error migration_error
-
-          raise RepositoryMigrationError, migration_error
-        end
-      end
     end
   end
 end

app/services/projects/hashed_storage/rollback_repository_service.rb

@@ -35,18 +35,6 @@ module Projects
 
         result
       end
-
-      private
-
-      def try_to_set_repository_read_only!
-        # Mitigate any push operation to start during migration
-        unless project.set_repository_read_only!
-          migration_error = "Target repository '#{old_disk_path}' cannot be made read-only as there is a git transfer in progress"
-          logger.error migration_error
-
-          raise RepositoryRollbackError, migration_error
-        end
-      end
     end
   end
 end

spec/services/projects/hashed_storage/migrate_repository_service_spec.rb

@@ -28,7 +28,7 @@ describe Projects::HashedStorage::MigrateRepositoryService do
       it 'fails when a git operation is in progress' do
         allow(project).to receive(:repo_reference_count) { 1 }
 
-        expect { service.execute }.to raise_error(Projects::HashedStorage::RepositoryMigrationError)
+        expect { service.execute }.to raise_error(Projects::HashedStorage::RepositoryInUseError)
       end
     end
 

spec/services/projects/hashed_storage/rollback_repository_service_spec.rb

@@ -30,7 +30,7 @@ describe Projects::HashedStorage::RollbackRepositoryService, :clean_gitlab_redis
       it 'fails when a git operation is in progress' do
         allow(project).to receive(:repo_reference_count) { 1 }
 
-        expect { service.execute }.to raise_error(Projects::HashedStorage::RepositoryRollbackError)
+        expect { service.execute }.to raise_error(Projects::HashedStorage::RepositoryInUseError)
       end
     end