Fix TODO encode? in create_sig

- n, e are `int`s, applied transformations make it `str`

- Crypto.Signature.PKCS1_v1_5.new [1] returns PKCS115_SigScheme, and its
  `sign()` method returns `str` [2]

- docs is OK: requires `nonce` to be `str`

- `create_sig` is not called with custom `nonce` argument anywhere in
  the code

[1] https://www.dlitz.net/software/pycrypto/api/2.6/Crypto.Signature.PKCS1_v1_5-module.html#new
[2] https://www.dlitz.net/software/pycrypto/api/2.6/Crypto.Signature.PKCS1_v1_5.PKCS115_SigScheme-class.html#sign
Fix TODO encode? in apache_configurator.

`s = Random.get_random_bytes(CONFIG.S_SIZE)`, so `s` is `str`.
Fix TODO encode? in acme.py