Improve rake task report on failure

It will clean up output from rake's "rake aborted!" reports on failures.
Failure in this case when sh method got exit status != 0

Before:
```shell
$:> rake
/Users/avakarev/.rvm/rubies/ruby-1.9.3-p392/bin/ruby -S bundle exec cucumber --format pretty
Feature: List
  In order to be informed how many there are items
  I want to be able to see all of those items as a list

  Scenario: List an items       # features/list.feature:5
    Given I am on the home page # features/step_definitions/web_steps.rb:1
      undefined local variable or method `go' for #<Object:0x007fef1510b240> (NameError)
      ./features/step_definitions/web_steps.rb:4:in `/^I am on the home page$/'
      features/list.feature:6:in `Given I am on the home page'
    Then I should see 4 items   # features/step_definitions/web_steps.rb:26

Failing Scenarios:
cucumber features/list.feature:5 # Scenario: List an items

1 scenario (1 failed)
2 steps (1 failed, 1 skipped)
0m1.500s
rake aborted!
Command failed with status (1): [/Users/avakarev/.rvm/rubies/ruby-1.9.3-p39...]
/Users/avakarev/.rvm/gems/ruby-1.9.3-p392/gems/cucumber-1.2.3/lib/cucumber/rake/task.rb:104:in `run'
/Users/avakarev/.rvm/gems/ruby-1.9.3-p392/gems/cucumber-1.2.3/lib/cucumber/rake/task.rb:197:in `block in define_task'
/Users/avakarev/.rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `eval'
/Users/avakarev/.rvm/gems/ruby-1.9.3-p392/bin/ruby_noexec_wrapper:14:in `<main>'
Tasks: TOP => default => features
(See full trace by running task with --trace)
```

After:
```shell
$:> rake
/Users/avakarev/.rvm/rubies/ruby-1.9.3-p392/bin/ruby -S bundle exec cucumber --format pretty
Feature: List
  In order to be informed how many there are items
  I want to be able to see all of those items as a list

  Scenario: List an items       # features/list.feature:5
    Given I am on the home page # features/step_definitions/web_steps.rb:1
      undefined local variable or method `go' for #<Object:0x007faed4b0a790> (NameError)
      ./features/step_definitions/web_steps.rb:4:in `/^I am on the home page$/'
      features/list.feature:6:in `Given I am on the home page'
    Then I should see 4 items   # features/step_definitions/web_steps.rb:26

Failing Scenarios:
cucumber features/list.feature:5 # Scenario: List an items

1 scenario (1 failed)
2 steps (1 failed, 1 skipped)
0m1.494s
```