setup.py: Add extras_require with development dependencies

Define extras_require with development packages. It's now possible to
use pip to install kernelci package in a regular or development version.
E.g.

pip install kernelci  # install regular version

pip install kernelci[dev]  # install development version

Signed-off-by: Michal Galka <[email protected]>

Author: Michal Galka

setup.py

@@ -80,5 +80,10 @@ def _list_files(path, match):
         "pytest",
         "pyyaml",
         "requests",
-    ]
+    ],
+    extras_require={
+        'dev': [
+            'pycodestyle'
+        ]
+    }
 )