libtar: don't set parent dir's context when extracting a file

Change-Id: I83e11b0119c47cb691d4e05ac1e5515aeafbdc87
Signed-off-by: Vojtech Bocek <vbocek@gmail.com>
Merge pull request #7 from omnirom/android-4.4

libtar: don't set parent dir's context when extracting a file