Add IncludeError exception and use it in CI config

lib/gitlab/ci/config.rb

@@ -13,10 +13,10 @@ module Gitlab
 
         @global = Entry::Global.new(@config)
         @global.compose!
-      rescue Loader::FormatError, Extendable::ExtensionError => e
+      rescue Loader::FormatError,
+             Extendable::ExtensionError,
+             External::Processor::IncludeError => e
         raise Config::ConfigError, e.message
-      rescue External::Processor::FileError => e
-        raise ::Gitlab::Ci::YamlProcessor::ValidationError, e.message
       end
 
       def valid?

lib/gitlab/ci/config/external/processor.rb

@@ -5,7 +5,8 @@ module Gitlab
     class Config
       module External
         class Processor
-          FileError = Class.new(StandardError)
+          IncludeError = Class.new(StandardError)
+          FileError = Class.new(IncludeError)
 
           def initialize(values, project, sha)
             @values = values

spec/lib/gitlab/ci/config_spec.rb

@@ -200,7 +200,7 @@ describe Gitlab::Ci::Config do
 
       it 'raises error YamlProcessor validationError' do
         expect { config }.to raise_error(
-          ::Gitlab::Ci::YamlProcessor::ValidationError,
+          described_class::ConfigError,
           "Local file 'invalid' is not valid."
         )
       end