Use dateutil.parser for parsing dates.

No more trying to remember format differences between my_activity.py
and my_reviews.py.

Change-Id: Iaac34529899a78aef3bd2e0742e674c8754f8afb
Reviewed-on: https://chromium-review.googlesource.com/655420Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>

my_activity.py

@@ -803,9 +803,9 @@ def main():
     else:
       begin, end = (get_week_of(datetime.today() - timedelta(days=1)))
   else:
-    begin = datetime.strptime(options.begin, '%m/%d/%y')
+    begin = dateutil.parser.parse(options.begin)
     if options.end:
-      end = datetime.strptime(options.end, '%m/%d/%y')
+      end = dateutil.parser.parse(options.end)
     else:
       end = datetime.today()
   options.begin, options.end = begin, end

my_reviews.py

@@ -17,6 +17,14 @@ import sys
 import auth
 import rietveld
 
+try:
+  import dateutil  # pylint: disable=import-error
+  import dateutil.parser
+  from dateutil.relativedelta import relativedelta
+except ImportError:
+  print 'python-dateutil package required'
+  exit(1)
+
 
 def username(email):
   """Keeps the username of an email address."""
@@ -358,8 +366,8 @@ def main():
 
   # Validate dates.
   try:
-    to_datetime(options.begin)
-    to_datetime(options.end)
+    options.begin = dateutil.parser.parse(options.begin).strftime('%Y-%m-%d')
+    options.end = dateutil.parser.parse(options.end).strftime('%Y-%m-%d')
   except ValueError as e:
     parser.error('%s: %s - %s' % (e, options.begin, options.end))