Do not use pkg_tars again in skia_app_container if run_commands_root or run_commands_skia is specified
Do not use pkg_tars again in skia_app_container if run_commands_root or
run_commands_skia is specified

This bug had 2 effects:
* Any changes to directories in pkg_tars by run_commands_root and
  run_commands_skia were overriden.
* Files/directories moved out of pkg_tars still existed causing slow
  builds of certain apps.

Bug: skia:12816
Change-Id: I2d9b7bff938f6f3bc3233aea9b28b81186509bc2
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/494856
Reviewed-by: Leandro Lovisolo <f558143c2568be8d55575d13f30a1fc5cb8009d5@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot