pushimage: fix GIT_REV in debug files

The code was writing out the CommandResult object instead of the contents
of the output.

Before:
	GIT_REV=<chromite.lib.cros_build_lib.CommandResult object at 0x1fb2e50>
After:
	GIT_REV=f74f7becdbd1b36c89ca8b46a19853b96c4a89ca

BUG=None
TEST=`./scripts/pushimage_unittest.py` passes

Change-Id: I73d2f3d14ed7b6a825e10c173f68e8404f176f66
Reviewed-on: https://chromium-review.googlesource.com/188653
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
diff --git a/scripts/pushimage_unittest.py b/scripts/pushimage_unittest.py
index f393346..fb5a9f9 100755
--- a/scripts/pushimage_unittest.py
+++ b/scripts/pushimage_unittest.py
@@ -5,12 +5,15 @@
 
 """Unittests for pushimage.py"""
 
+from __future__ import print_function
+
 import logging
 import os
 import sys
 
 sys.path.insert(0, os.path.join(os.path.dirname(os.path.realpath(__file__)),
                                 '..', '..'))
+from chromite.lib import cros_build_lib
 from chromite.lib import cros_test_lib
 from chromite.lib import git
 from chromite.lib import gs
@@ -120,7 +123,8 @@
 
     # Minor optimization -- we call this for logging purposes in the main
     # code, but don't really care about it for testing.  It just slows us.
-    self.PatchObject(git, 'RunGit')
+    self.PatchObject(git, 'RunGit',
+                     return_value=cros_build_lib.CommandResult(output='1234\n'))
 
   def testBasic(self):
     """Simple smoke test"""
@@ -157,6 +161,7 @@
     content = m.call_args_list[0][0][1]
     self.assertIn('USER=', content)
     self.assertIn('HOSTNAME=', content)
+    self.assertIn('GIT_REV=1234', content)
     self.assertIn('\n', content)
 
   def testTbsUpload(self):