Add missing imports in powerline-config

They matter when script is used without properly installing powerline, so that 
importing `powerline.bindings.config` does not work.

scripts/powerline-config

@@ -7,6 +7,8 @@ import argparse
 try:
 	import powerline.bindings.config as config
 except ImportError:
+	import sys
+	import os
 	sys.path.append(os.path.dirname(os.path.dirname(os.path.abspath(os.path.realpath(__file__)))))
 	import powerline.bindings.config as config  # NOQA