Blacklist weak and slow cipher suites in TLS

Per the comments in cmd.py:

Instate a cipher suite that bans a series of weak and slow ciphers.
Both RC4 (weak) DES (weak and slow) have been seen with default cipher
suites on both Ubuntu Raring and Ubuntu Precise, respectively.

Only Python 2.7+ possesses the 'ciphers' keyword to wrap_socket.