Add cr clobber command.

This patch adds a 'clobber' command to cr which deletes all files
in the current output directory (except for the cr config file).

BUG=

Review URL: https://codereview.chromium.org/703533003

Cr-Commit-Position: refs/heads/master@{#302581}

tools/cr/cr/commands/clobber.py

+# Copyright 2014 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""A module for the clobber command."""
+
+import os
+import shutil
+
+import cr
+
+
+class ClobberCommand(cr.Command):
+  """The implementation of the clobber command.
+
+  The clobber command removes all generated files from the output directory.
+  """
+
+  def __init__(self):
+    super(ClobberCommand, self).__init__()
+    self.help = 'Clobber the current output directory'
+    self.description = ("""
+        This deletes all generated files from the output directory.
+        """)
+
+  def Run(self):
+    self.Clobber()
+
+  @classmethod
+  def Clobber(cls):
+    """Performs the clobber."""
+    build_dir = cr.context.Get('CR_BUILD_DIR')
+    verbose = cr.context.verbose >= 3 or cr.context.dry_run
+    delete = not cr.context.dry_run
+    print 'Clobbering...'
+    for f in os.listdir(build_dir):
+      if f == cr.base.client.CLIENT_CONFIG_PATH:
+        continue
+      path = os.path.join(build_dir, f)
+      if os.path.isfile(path):
+        if verbose:
+          print 'Delete file %s' % path
+        if delete:
+          os.unlink(path)
+      elif os.path.isdir(path):
+        if verbose:
+          print 'Delete folder %s' % path
+        if delete:
+          shutil.rmtree(path)
+    print 'Done'