Install Riak (1.4.2-1) from official Basho APT repository

@joshk: as discussed today, I let you select/adapt `vm.args` and `config.app`, the way Riak users may prefer...

The first commit include default `vm.args` and `config.app` files provided by Basho `riak` package.
In the second commit, I include the Travis legacy configuration (attention: these files were generated in my locat test environment, 100% match with effective production should therefore be verified).

I successfully validated Travis settings (ff169a5) by building https://github.com/basho/riak-python-client in my local box, against python 2.6 (I didn't try 2.7 since recent builds are failing on travis-ci.org):

```
vagrant@precise64:~/tests/riak-python-client$ ./setup.py test
running test
Searching for unittest2
Reading https://pypi.python.org/simple/unittest2/
...
test_set_non_default_tmp_dir (riak.tests.test_server_test.TestServerTestCase) ... ok
test_set_ring_state_dir (riak.tests.test_server_test.TestServerTestCase) ... ok

----------------------------------------------------------------------
Ran 250 tests in 36.789s

OK
```

**Small Note:** 

this cookbook does not control the `ulimit` settings, which is not a problem as long as it is used in combination with other cookbooks (like `travis_build_environment`) that take care of this part. If you see a message like following, you may need to tweak your global system limits (e.g. max open files):

```
vagrant@vagrant:~$ sudo service riak start
Node 'riak@127.0.0.1' not responding to pings.
!!!!
!!!! WARNING: ulimit -n is 1024; 4096 is the recommended minimum.
!!!!
```

//cc @seancribbs @roidrage @michaelklishin