Add acceptance to the rake tasks (#7).

Rakefile

@@ -7,3 +7,23 @@ require 'puppet-strings/tasks'
 Blacksmith::RakeTask.new do |t|
   t.tag_pattern = '%s'
 end
+
+desc '[CI Only] Run beaker, but only for pull requests or for release branches.'
+task :acceptance do
+  skip = true
+  travis_branch = ENV['TRAVIS_BRANCH']
+  travis_event_type = ENV['TRAVIS_EVENT_TYPE']
+
+  if travis_event_type == 'pull_request'
+    skip = false
+  elsif travis_event_type == 'push'
+    skip = false if travis_branch =~ /^release-/ || travis_branch =~ /^hotfix-/
+  end
+
+  if skip
+    puts 'Skipping acceptance tests.'
+    exit(0)
+  else
+    Rake::Task['beaker'].invoke
+  end
+end