Make features global configuration proof

If a `~/.config/rspec/options` file contains the following:

    --color
    --profile 2
    --format progress

a number of features fail, since options are picked up and used by the
code under test.

Resetting `XDG_CONFIG_HOME` for those features isolates the global
configuration.

Author: pirj

features/command_line/init.feature

@@ -25,6 +25,7 @@ Feature: `--init` option
   Scenario: Accept and use the recommended settings in `spec_helper` (which are initially commented out)
     Given I have a brand new project with no files
       And I have run `rspec --init`
+      And I unset XDG_CONFIG_HOME environment var
      When I accept the recommended settings by removing `=begin` and `=end` from `spec/spec_helper.rb`
       And I create "spec/addition_spec.rb" with the following content:
         """ruby

features/command_line/warnings_option.feature

@@ -25,5 +25,6 @@ Feature: `--warnings` option (run with warnings enabled)
         end
       end
       """
+    And I unset XDG_CONFIG_HOME environment var
     When I run `rspec example_spec.rb`
     Then the output should not contain "warning"

features/configuration/profile.feature

@@ -73,6 +73,7 @@ Feature: Profile examples
       """
 
   Scenario: By default does not show profile
+    Given I unset XDG_CONFIG_HOME environment var
     When I run `rspec spec`
     Then the examples should all pass
     And the output should not contain "example 1"
@@ -92,6 +93,7 @@ Feature: Profile examples
       """ruby
       RSpec.configure { |c| c.profile_examples = true }
       """
+    And I unset XDG_CONFIG_HOME environment var
     When I run `rspec spec`
     Then the examples should all pass
     And the output should contain "Top 10 slowest examples"

features/formatters/configurable_colors.feature

@@ -27,5 +27,6 @@ Feature: Configurable colors
         end
       end
       """
-      When I run `rspec custom_failure_color_spec.rb --format progress`
-      Then the failing example is printed in magenta
+    And I unset XDG_CONFIG_HOME environment var
+    When I run `rspec custom_failure_color_spec.rb --format progress`
+    Then the failing example is printed in magenta

features/step_definitions/additional_cli_steps.rb

@@ -238,6 +238,13 @@
   end
 end
 
+Given(/^I unset XDG_CONFIG_HOME environment var$/) do
+  step %q{I set the environment variables to:}, table(%{
+  | variable        | value |
+  | XDG_CONFIG_HOME |       |
+  })
+end
+
 module Normalization
   def normalize_failure_output(text)
     whitespace_normalized = text.lines.map { |line| line.sub(/\s+$/, '').sub(/:in .*$/, '') }.join