Fix md5sum.py crashing when trying to delete non-existent md5sum directory

"rm -rf foo/" fails, but "rm -rf foo" succeeds

BUG=

Review URL: https://codereview.chromium.org/1332373002

Cr-Original-Commit-Position: refs/heads/master@{#348415}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: a9d40e8aedcad7433eed48f3437f39f0ccfc2a86

android/devil/android/md5sum.py

@@ -10,8 +10,8 @@ from devil.android import device_errors
 from devil.utils import cmd_helper
 from pylib import constants
 
-MD5SUM_DEVICE_LIB_PATH = '/data/local/tmp/md5sum/'
-MD5SUM_DEVICE_BIN_PATH = MD5SUM_DEVICE_LIB_PATH + 'md5sum_bin'
+MD5SUM_DEVICE_LIB_PATH = '/data/local/tmp/md5sum'
+MD5SUM_DEVICE_BIN_PATH = MD5SUM_DEVICE_LIB_PATH + '/md5sum_bin'
 
 _STARTS_WITH_CHECKSUM_RE = re.compile(r'^\s*[0-9a-fA-F]{32}\s+')
 

android/devil/android/md5sum_test.py

@@ -225,7 +225,7 @@ class Md5SumTest(unittest.TestCase):
                         out['/storage/emulated/legacy/test/file.dat'])
       self.assertEquals(3, len(device.RunShellCommand.call_args_list))
       device.adb.Push.assert_called_once_with(
-          'test/out/directory/md5sum_dist', '/data/local/tmp/md5sum/')
+          'test/out/directory/md5sum_dist', '/data/local/tmp/md5sum')
 
 
 if __name__ == '__main__':