adb: Do not use fs_config unless we are root (try 2).

This enables fs_config for /data when pushing files as root. Also,
without this, adb push to /tmp fails as the shell user.

When pushing to a directory that does not have an explicit fs_config,
such as /data/local/tmp or /tmp, use the original file mode.

Bug: 171233429
Bug: 311263616
Change-Id: Ied805bc3912ea0b4e1691127b5032aef632f85fd