On-device signing: reject everything that's not a regular file/dir.

We shouldn't allow anything else in the artifacts output directory.

Bug: 192061595
Test: TEST_MAPPING
Change-Id: I1be9dfd7982d543a8979ac3a34551bd5449004f7
Merged-In: I1be9dfd7982d543a8979ac3a34551bd5449004f7
1 file changed