message: getdeps: correctly handle the install_dir value
  Summary:
  We were computing `SCRATCH/install` and hashing based on that value,
  but the build stuff was later computing `SCRATCH/installed` and passing that
  to the builders.
  Fixup the mismatch.
diff: @@ -59,7 +59,7 @@ class BuildOptions(object):
  num_jobs = multiprocessing.cpu_count()
  if not install_dir:
  - install_dir = os.path.join(scratch_dir, "install")
  + install_dir = os.path.join(scratch_dir, "installed")
  self.project_hashes = None
  for p in ["../deps/github_hashes", "../project_hashes"]:
  @@ -157,7 +157,7 @@ class BuildOptions(object):
  directory = "%s-%s" % (manifest.name, hash)
  build_dir = os.path.join(self.scratch_dir, "build", directory)
  - inst_dir = os.path.join(self.scratch_dir, "installed", directory)
  + inst_dir = os.path.join(self.install_dir, directory)
  return {"build_dir": build_dir, "inst_dir": inst_dir, "hash": hash}
  