You have to execute vagrant up first

I put in the `???` because it still doesn't work for me.

```pytb
$fab vagrant prepare
[localhost] local: vagrant ssh-config
[127.0.0.1:2222] Executing task 'prepare'
[127.0.0.1:2222] sudo: apt-get -qq update
Traceback (most recent call last):
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/main.py", line 739, in main
    *args, **kwargs
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/tasks.py", line 317, in execute
    multiprocessing
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/tasks.py", line 213, in _execute
    return task.run(*args, **kwargs)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/tasks.py", line 123, in run
    return self.wrapped(*args, **kwargs)
  File "/Users/aaronmeurer/Documents/Python/sympy/sympy/release/fabfile.py", line 8, in prepare
    prepare_apt()
  File "/Users/aaronmeurer/Documents/Python/sympy/sympy/release/fabfile.py", line 18, in prepare_apt
    sudo("apt-get -qq update")
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/network.py", line 535, in host_prompting_wrapper
    return func(*args, **kwargs)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/operations.py", line 1065, in sudo
    stderr=stderr, timeout=timeout
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/operations.py", line 889, in _run_command
    channel=default_channel(), command=wrapped_command, pty=pty,
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/state.py", line 380, in default_channel
    chan = _open_session()
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/state.py", line 372, in _open_session
    return connections[env.host_string].get_transport().open_session()
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/network.py", line 109, in __getitem__
    self.connect(key)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/network.py", line 101, in connect
    self[key] = connect(user, host, port, sock)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/fabric/network.py", line 354, in connect
    sock=sock
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/client.py", line 337, in connect
    self._auth(username, password, pkey, key_filenames, allow_agent, look_for_keys)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/client.py", line 457, in _auth
    key = pkey_class.from_private_key_file(key_filename, password)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/pkey.py", line 198, in from_private_key_file
    key = cls(filename=filename, password=password)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/rsakey.py", line 51, in __init__
    self._from_private_key_file(filename, password)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/rsakey.py", line 163, in _from_private_key_file
    data = self._read_private_key_file('RSA', filename, password)
  File "/Users/aaronmeurer/anaconda/envs/sympy-release/lib/python2.7/site-packages/paramiko/pkey.py", line 279, in _read_private_key_file
    f = open(filename, 'r')
IOError: [Errno 2] No such file or directory: '"/Users/aaronmeurer/.vagrant.d/insecure_private_key"'
```