option to omit %check (and all test related BuildRequires)

Sometimes packaging a Python module in and of itself is simple, but the tests it has bundled introduces a deep stack of required modules. I.e.:

```
'tests_require': [
'coverage!=4.4,>=4.0',
'fixtures>=3.0.0',
'hacking!=0.13.0,<0.14,>=0.12.0',
'mock>=2.0',
'python-subunit>=0.0.18',
'sphinx!=1.6.1,>=1.5.1',
'oslosphinx>=4.7.0',
'six>=1.9.0',
'testrepository>=0.0.18',
'testresources>=0.2.4',
'testscenarios>=0.4',
'testtools>=1.4.0',
'virtualenv>=13.1.0'
],
```

Sometimes I just need to get the module packaged without diving deeply into a rabbit-hole of building a deep stack of RPMs just to satisfy testing. I am happy to trust that upstream has tested sufficiently and don't need my RPM packaging to do it also. Yes, I realise that I am risking building a broken module if I don't run tests. I'm OK to take on that risk for the short-term gain.

An option to tell `pyp2rpm` that this is what I want would be nice for such Q&D builds.

Ideally all PyPI-RPM modules would have working tests and perhaps once I have provided a working RPM I will go back and build the test stack also, but I need avoid having to build this stack gating other tasks that depend on the RPM.

Thoughts?