kleaf: Use action_config not tool_path.

... so we can rely on actual File objects, not relative
paths.

This change allows the deletion of the kleaf/parent symlinks
later.

This change is in response to
bazelbuild/bazel#8438 (comment)

Test: TH
Bug: bazelbuild/bazel#8438
Bug: 280012530
Change-Id: Ie9846847167e5a0c2b1cb1dde5a7c82a17cd3862