hardware_DiskSize,SsdDetection: fix hardware root dev discovery

client/site_tests/hardware_DiskSize/hardware_DiskSize.py

 # 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.
 
 import logging
+import os
 import re
 
 from autotest_lib.client.bin import test, utils
 from autotest_lib.client.common_lib import error
 
 class hardware_DiskSize(test.test):
     version = 1
 
     def run_once(self):
-        cmdline = file('/proc/cmdline').read()
-        match = re.search(r'root=/dev/([^ ]+)', cmdline)
-        if not match:
-            raise error.TestError('Unable to find the root partition')
-        device = match.group(1)[:-1]
+        devnode = utils.system_output('rootdev -s -d -i')
+        device = os.path.basename(devnode)
 
         for line in file('/proc/partitions'):
             try:
                 major, minor, blocks, name = re.split(r' +', line.strip())
             except ValueError:
                 continue
             # TODO(waihong@): Check if this works on ARM.
             if name == device:
                 blocks = int(blocks)
                 break
         else:
             raise error.TestError('Unable to determine main disk size')
 
         # Capacity of a hard disk is quoted with SI prefixes, incrementing by
         # powers of 1000, instead of powers of 1024.
         gb = blocks * 1024.0 / 1000.0 / 1000.0 / 1000.0
         self.write_perf_keyval({"gb_main_disk_size": gb})
         logging.info("DiskSize: %.3f GB" % gb)