Use 0777 instead of FileInfo() for dirs.

Golang's FileInfo() implementation recognizes FAT filesystem directories
correctly, but doesn't actually add executable bits, which essentially
makes them inaccessible. Use 0777 when we know we're dealing with
directories.

Fixes: 153207404
Test: manually tested with an aar file with FAT permission bits.
Change-Id: Ie9f5320bc44d24b2f9d54d4036bb1747456655bb