Fix the print of the rebase error message, and make the output prettier too.

For some reason .output doesn't throw an AttributeError, but returns None ,
instead. .stdout is the correct attribute.

R=agable@chromium.org
BUG=

Review URL: https://codereview.chromium.org/212493003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@259695 0039d316-1c4b-4281-b951-d872f2087c98

git_common.py

@@ -432,7 +432,7 @@ def rebase(parent, start, branch, abort=False):
   except subprocess2.CalledProcessError as cpe:
     if abort:
       run('rebase', '--abort')
-    return RebaseRet(False, cpe.output)
+    return RebaseRet(False, cpe.stdout)
 
 
 def remove_merge_base(branch):

git_rebase_update.py

@@ -137,6 +137,9 @@ def rebase_branch(branch, parent, start_hash):
       else:
         # rebase and leave in mid-rebase state.
         git.rebase(parent, start_hash, branch)
+        print "Failed!"
+        print
+        print "Here's what git-rebase had to say:"
         print squash_ret.message
         print
         print textwrap.dedent(