fix: exclude tests folder when install package

[apbard]

You should exclude tests from the wheel. If it gets installed it produces weird errors.

_____________________________________________________________________________________________ ERROR collecting  _____________________________________________________________________________________________
../../.local/lib/python3.5/site-packages/py/_path/common.py:377: in visit
    for x in Visitor(fil, rec, ignore, bf, sort).gen(self):
../../.local/lib/python3.5/site-packages/py/_path/common.py:418: in gen
    dirs = self.optsort([p for p in entries
../../.local/lib/python3.5/site-packages/py/_path/common.py:419: in <listcomp>
    if p.check(dir=1) and (rec is None or rec(p))])
../../.local/lib/python3.5/site-packages/_pytest/main.py:511: in _recurse
    ihook = self.gethookproxy(path)
../../.local/lib/python3.5/site-packages/_pytest/main.py:413: in gethookproxy
    my_conftestmodules = pm._getconftestmodules(fspath)
../../.local/lib/python3.5/site-packages/_pytest/config/__init__.py:383: in _getconftestmodules
    mod = self._importconftest(conftestpath)
../../.local/lib/python3.5/site-packages/_pytest/config/__init__.py:412: in _importconftest
    raise ConftestImportFailure(conftestpath, sys.exc_info())
E   _pytest.config.ConftestImportFailure: ImportError("No module named 'mock'",)
E     File "/home/apbardelli/.local/lib/python3.5/site-packages/_pytest/assertion/rewrite.py", line 216, in load_module
E       py.builtin.exec_(co, mod.__dict__)
E     File "/home/apbardelli/Projects/arc-exercise-modelling/src/tests/session_handlers/conftest.py", line 30, in <module>
E       from tests.test_common_functions import DataGenerationUtils
E     File "/usr/local/lib/python3.5/dist-packages/tests/__init__.py", line 1, in <module>
E       import mock  # noqa

[relekang]

Thanks, since this deleted a few necessary files I just made the needed fix in 3e41e91