Vagrantfile: Install Android SDK with built-tools

With the current Android SDK installation in our Vagrant file,
hmp_parity.py tests fail with:

======================================================================
ERROR: test suite for <class 'hmp_parity.ForkMigration'>
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/nose/suite.py", line 208, in run
    self.setUp()
  File "/usr/lib/python2.7/dist-packages/nose/suite.py", line 291, in setUp
    self.setupContext(ancestor)
  File "/usr/lib/python2.7/dist-packages/nose/suite.py", line 314, in setupContext
    try_run(context, names)
  File "/usr/lib/python2.7/dist-packages/nose/util.py", line 471, in try_run
    return func()
  File "/vagrant/tests/eas/hmp_parity.py", line 125, in setUpClass
    cls.env = TestEnv(test_conf=TEST_CONF)
  File "/home/vagrant/lisa/libs/utils/env.py", line 189, in __init__
    self._init()
  File "/home/vagrant/lisa/libs/utils/env.py", line 260, in _init
    self._init_target(force)
  File "/home/vagrant/lisa/libs/utils/env.py", line 446, in _init_target
    modules = self.__modules)
  File "/home/vagrant/lisa/libs/devlib/devlib/target.py", line 720, in __init__
    shell_prompt=shell_prompt)
  File "/home/vagrant/lisa/libs/devlib/devlib/target.py", line 171, in __init__
    self.connect()
  File "/home/vagrant/lisa/libs/devlib/devlib/target.py", line 740, in connect
    adb_disconnect(device)
  File "/home/vagrant/lisa/libs/devlib/devlib/utils/android.py", line 287, in adb_disconnect
    _check_env()
  File "/home/vagrant/lisa/libs/devlib/devlib/utils/android.py", line 447, in _check_env
    _env = _initialize_with_android_home(_AndroidEnvironment())
  File "/home/vagrant/lisa/libs/devlib/devlib/utils/android.py", line 405, in _initialize_with_android_home
    _init_common(env)
  File "/home/vagrant/lisa/libs/devlib/devlib/utils/android.py", line 429, in _init_common
    raise HostError(msg.format(env.android_home))
HostError: ANDROID_HOME (/vagrant/tools/android-sdk-linux) does not appear to have valid Android SDK install
                 (cannot find build-tools)

Install build-tools to please devlib.