Change Android retry logic - always retry 3 times.

Android retry logic currently changes based on number of
devices.  This means that test runs are more flaky when only
one device is attached.  Change this to always retry 3 times.

BUG=175653
NOTRY=True

Review URL: https://chromiumcodereview.appspot.com/12207172

git-svn-id: http://src.chromium.org/svn/trunk/src/build@182420 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/base/base_test_sharder.py

@@ -11,6 +11,10 @@ from pylib.base.test_result import TestResults
 from pylib.forwarder import Forwarder
 
 
+# Number of times we retry a test suite in case of failure.
+NUM_RETRIES = 3
+
+
 def _ShardedTestRunnable(test):
   """Standalone function needed by multiprocessing.Pool."""
   log_format = '[' + test.device + '] # %(asctime)-15s: %(message)s'
@@ -54,7 +58,7 @@ class BaseTestSharder(object):
     # We should differentiate between these. Otherwise, blindly retrying tests
     # might mask test/product flakiness. For type 2, we should follow the
     # general chrome best practices.
-    self.retries = len(self.attached_devices)
+    self.retries = NUM_RETRIES
     self.tests = []
     self.build_type = build_type