[autoscaler] Fix custom node resources on head

[ijrsvt]

Why are these changes needed?

• Without these changes, custom head resources do not work for the head node!

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://docs.ray.io/en/master/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failures at https://flakey-tests.ray.io/
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested :(

[ericl]

//python/ray/tests:test_cli FAILED in 3 out of 3 in 177.3s
Stats over 3 runs: max = 177.3s, min = 176.4s, avg = 176.7s, dev = 0.4s
/home/travis/.cache/bazel/_bazel_travis/b88c129a127452fc94033a29d9f90e20/execroot/com_github_ray_project_ray/bazel-out/k8-opt/testlogs/python/ray/tests/test_cli/test.log
/home/travis/.cache/bazel/_bazel_travis/b88c129a127452fc94033a29d9f90e20/execroot/com_github_ray_project_ray/bazel-out/k8-opt/testlogs/python/ray/tests/test_cli/test_attempts/attempt_1.log
/home/travis/.cache/bazel/_bazel_travis/b88c129a127452fc94033a29d9f90e20/execroot/com_github_ray_project_ray/bazel-out/k8-opt/testlogs/python/ray/tests/test_cli/test_attempts/attempt_2.log