Make bot_update.py print git version it uses.

R=iannucci@chromium.org, dnj@chromium.org
BUG=647446

Review-Url: https://codereview.chromium.org/2344313002

recipe_modules/bot_update/resources/bot_update.py

@@ -941,6 +941,10 @@ def prepare(options, git_slns, active):
 
 
 def checkout(options, git_slns, specs, revisions, step_text, shallow):
+  print 'Checking git version...'
+  ver = git('version').strip()
+  print 'Using %s' % ver
+
   first_sln = git_slns[0]['name']
   dir_names = [sln.get('name') for sln in git_slns if 'name' in sln]
   try: