integrating py.test into setuptools (sonic-net#103)

* integrating py.test into setuptools
* removed test dependencies from extras_require and add it as test_require

Author: samaity

setup.cfg

@@ -0,0 +1,2 @@
+[aliases]
+test=pytest

setup.py

@@ -18,10 +18,11 @@
 setup(
     name='asyncsnmp',
     install_requires=dependencies,
+    setup_requires=["pytest-runner"],
+    tests_require=test_deps,
     version='2.1.0',
     packages=find_packages('src'),
     extras_require={
-        'testing': test_deps,
         'high_perf': high_performance_deps,
     },
     license='Apache 2.0',