As reported by reef-paladin.  git.lock file needs cleanup

https://uberchromegw.corp.google.com/i/chromeos/builders/reef-paladin/builds/686

fatal: Unable to create 
'/b/build_internal/scripts/slave/.recipe_deps/build/.git/index.lock': File exists.
Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.
Traceback (most recent call last):
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipes.py", line 646, in <module>
    ret = main()
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipes.py", line 597, in main
    deps_path=args.deps_path, overrides=args.project_override)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/package.py", line 634, in create
    RootRepoSpec(proto_file), False)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/package.py", line 645, in _create_package
    return self._create_from_spec(repo_spec, package_spec, overriding)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/package.py", line 666, in _create_from_spec
    dep_package = self._create_package(dep_repo, overriding)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/package.py", line 643, in _create_package
    repo_spec.checkout(self._context)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/package.py", line 199, in checkout
    self.repo, self.revision, checkout_dir, context.allow_fetch)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/util.py", line 223, in wrapper
    return f(*args, **kwargs)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/fetch.py", line 160, in checkout
    git('reset', '-q', '--hard', revision)
  File "/b/build_internal/scripts/slave/.recipe_deps/recipe_engine/recipe_engine/fetch.py", line 117, in __call__
    subcommand, e.message,))
GitError: Git "reset" failed: 
Uncaught exception (GitError): Git "reset" failed: