Python's cffi package is not installed as dependency on OpenBSD

[oherrala]

In OpenBSD-current (snapshot 2017-06-13 and Python 3.6.1), Python's cffi package is missing and TryTLS doesn't work.

It can be installed from OpenBSD package py-cffi (for Python 2) or py3-cffi for Python 3. But maybe oscrypto package should depend on it if it's the one needing it.

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto_cffi.py", line 13, in <module>
    from cffi import FFI
ModuleNotFoundError: No module named 'cffi'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto.py", line 8, in <module>
    from ._libcrypto_cffi import (
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto_cffi.py", line 16, in <module>
    raise FFIEngineError('Error importing cffi')
oscrypto._ffi.FFIEngineError: Error importing cffi

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto_ctypes.py", line 258, in <module>
    libcrypto.EVP_MD_CTX_new.argtypes = []
  File "/usr/local/lib/python3.6/ctypes/__init__.py", line 361, in __getattr__
    func = self.__getitem__(name)
  File "/usr/local/lib/python3.6/ctypes/__init__.py", line 366, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: Unable to resolve symbol

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/bin/trytls", line 11, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.6/site-packages/trytls/runner.py", line 177, in main
    bundle = bundles.load_bundle(bundle_name)
  File "/usr/local/lib/python3.6/site-packages/trytls/bundles/__init__.py", line 11, in load_bundle
    return entry.load()
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2268, in load
    return self.resolve()
  File "/usr/local/lib/python3.6/site-packages/pkg_resources/__init__.py", line 2274, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/usr/local/lib/python3.6/site-packages/trytls/bundles/https.py", line 15, in <module>
    from ..gencert import gencert
  File "/usr/local/lib/python3.6/site-packages/trytls/gencert.py", line 3, in <module>
    from oscrypto import asymmetric
  File "/usr/local/lib/python3.6/site-packages/oscrypto/asymmetric.py", line 15, in <module>
    from .kdf import pbkdf2, pbkdf2_iteration_calculator
  File "/usr/local/lib/python3.6/site-packages/oscrypto/kdf.py", line 9, in <module>
    from .util import rand_bytes
  File "/usr/local/lib/python3.6/site-packages/oscrypto/util.py", line 14, in <module>
    from ._openssl.util import rand_bytes
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/util.py", line 6, in <module>
    from ._libcrypto import libcrypto, libcrypto_version_info, handle_openssl_error
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto.py", line 14, in <module>
    from ._libcrypto_ctypes import (
  File "/usr/local/lib/python3.6/site-packages/oscrypto/_openssl/_libcrypto_ctypes.py", line 668, in <module>
    raise FFIEngineError('Error initializing ctypes')
oscrypto._ffi.FFIEngineError: Error initializing ctypes