HOTFIX: Fix unicode error in merge script.

The merge script builds up a big command array and sometimes
this contains both unicode and ascii strings. This doesn't work
if you try to join them into a single string. Longer term a solution
is to go and make sure the source of all strings is unicode.

This patch provides a simpler solution... just print the array
rather than joining. I actually prefer printing an array here
anyways since joining on spaces is lossy in the case of arguments
that themselves contain spaces.

Author: Patrick Wendell <pwendell@gmail.com>

Closes #2645 from pwendell/merge-script and squashes the following commits:

167b792 [Patrick Wendell] HOTFIX: Fix unicode error in merge script.

dev/merge_spark_pr.py

@@ -73,11 +73,10 @@ def fail(msg):
 
 
 def run_cmd(cmd):
+    print cmd
     if isinstance(cmd, list):
-        print " ".join(cmd)
         return subprocess.check_output(cmd)
     else:
-        print cmd
         return subprocess.check_output(cmd.split(" "))