From source builds do not include embedded libssh2 in package #51

Bug reports

Steps to reproduce:

1. Run pip install ssh2-python on Travis when using PyPy. (I have tried with both 2.7 and 3.5 versions of PyPy 6.0.
2. In the pypy interpreter, try to run from ssh2.session import Session.

3.  from ssh2.session import Session
    E   ImportError: unable to load extension module '/home/travis/virtualenv/pypy2.7-6.0.0/
    site-packages/ssh2/session.pypy-41.so': libssh2.so.1: cannot open shared object file: 
    No such file or directory
   

I also tried installing the libssh2-1-dev package on Travis first, and got a slightly different error message:

ImportError: unable to load extension module '/home/travis/virtualenv/pypy2.7-6.0.0/
             site-packages/ssh2/session.pypy-41.so': /home/travis/virtualenv/pypy2.7-6.0.0/site-
             packages/ssh2/session.pypy-41.so: undefined symbol: libssh2_session_set_last_error

Expected behaviour: Able to import Session properly in PyPy.

Actual behaviour: Exceptions above.

Additional info: Ubuntu 16.04. You can see multiple failed attempts on Travis (as part of a project that was trying to use parallel-ssh here and here.