[WIP] Hotfix for the `serverspec`'s bahaviour change.

Serverspec offers the information about the target server,
providing `os` hashes.

Noticed that `os[:release]` does not return release names,
such as "precise", but rather "12.04".

Due to this behavioural change, tests breaks.
Change the condition to follow the `serverspec`'s behavioural change.

Serverspec offers the information about the target server,
providing `os` hashes.

Noticed that `os[:release]` no longer returns the release names,
such as "precise", but rather "12.04".

Due to this behavioural change, tests breaks.

This commit is intended to fix this problem:

```
diff --git a/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb b/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
index 38895bf..1b8ce0f 100644
--- a/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
+++ b/site-cookbooks/base/test/integration/default/serverspec/packages_spec.rb
@@ -24,7 +24,7 @@ describe package('ruby') do
   it { should be_installed }
 end

-if os[:release].include?("precise")
+if os[:release] == "12.04"
   describe package('rubygems') do
     it { should be_installed }
   end
```
Merge pull request #143 from kazu634/hotfix-for-base-test

Hotfix for the `serverspec`'s bahaviour change.
[common] Install `kitchen-docker` and update `Gemfile.lock`.
[common] Create `Dockerfile` for Ubuntu 12.04.
[common] Create `Dockerfile` for Ubuntu 14.04.
[base] Modify `.kitchen.yml` to support `docker` testing.
[base] Modify test, due to the timezone config difference between Japanese and US. version of Ubuntu.
[common] Add `test` rake task.

```
diff --git a/tasks/tests/ci.rake b/tasks/tests/ci.rake
new file mode 100755
index 0000000..a612849
--- /dev/null
+++ b/tasks/tests/ci.rake
@@ -0,0 +1,12 @@
+#!/usr/bin/env rake
+
+require 'rake'
+
+desc "Run CI tests."
+task :test do
+  cookbooks = `git diff --name-only master..$(git symbolic-ref HEAD) | grep site-cookbooks | cut -f 2 -d / | awk '!a[$0]++'`
+
+  cookbooks.split('\n').each do |cookbook|
+    puts "cd #{PROJ_ROOT}/site-cookbook/#{cookbook}"
+  end
+end
```
[common] Modify `circle.yml` to execute tests.