[autotest] Pull suite sharding factor from global_config.ini

Instead of hard-coding a sharding factor in each suite control file,
put a default one in global_config.ini.  Allow overrides.

BUG=chromium-os:26431
TEST=unit
TEST=use dev_harness to run control.bvt, see that it schedules 5 reimaging jobs.
STATUS=Fixed

Change-Id: Ife5a1d117701785530b040ab9b08796b06d57f76
Reviewed-on: https://gerrit.chromium.org/gerrit/15975
Tested-by: Chris Masone <cmasone@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Chris Masone <cmasone@chromium.org>
diff --git a/test_suites/control.dummy b/test_suites/control.dummy
index 38a2193..fceda9e 100644
--- a/test_suites/control.dummy
+++ b/test_suites/control.dummy
@@ -1,4 +1,4 @@
-# Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
+# Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
@@ -24,6 +24,6 @@
 reimager = dynamic_suite.Reimager(job.autodir)
 
 if (reimager.skip(globals()) or
-    reimager.attempt(build, 1, board, job.record)):
+    reimager.attempt(build, board, job.record, num=1)):
     bvt = dynamic_suite.Suite.create_from_name(suite_tag, job.autodir)
     bvt.run_and_wait(build, job.record, add_experimental=True)