Fix tests that rely on rootdev specifying a real block device.

client/site_tests/hardware_ExternalDrives/control

 # Copyright (c) 2010 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.
 TIME='MEDIUM'
 AUTHOR = 'The Chromium OS Authors'
 DOC = """
 External storage test suite.
 
 Tests external storage (USB flash drive / card reader with SD-card inserted)
 performance using several benchmark tools.
 """
 NAME = 'hardware_ExternalDrives'
 PURPOSE = 'Benchmark external storage devices.'
 CRITERIA = 'This test is a benchmark.'
 TEST_CLASS = 'hardware'
 TEST_CATEGORY = 'Performance'
 TEST_TYPE = 'client'
 VERSION = '1'
 
 import os, re
 
 from autotest_lib.client.bin import utils
 from autotest_lib.client.common_lib import error, site_ui
 
 
 def find_root_dev():
-    rootdev = utils.system_output('rootdev')
-    return os.path.basename(rootdev[:-1])
+    rootdev = utils.system_output('rootdev -s -d')
+    return os.path.basename(rootdev)
 
 
 def find_all_storage_dev():
     lssys = utils.run('ls -d /sys/block/sd*')
     devices = lssys.stdout.rsplit('\n')
     new_devices = [os.path.basename(d.rstrip()) for d in devices if d]
     return new_devices
 
 
 num_retry = 3
@@ skipping 13 matching lines @@
             if os.path.exists(devpath):
                 job.run_test('hardware_StorageFio', dev=devpath, tag=device)
         break
     else:
         result = dialog.get_result()
         num_retry -= 1;
 
 else:
     raise error.TestError('Unable to find a USB flash drive and a SD-card')