Fix remaining file related CTS Test failures.

Most failures were because tests were trying to
open files relative to the current working directory,
instead of in a temp directory.

FileTest was failing because it didn't construct
paths correctly. It would add an additional separator
char even if the path already ended with one.

bug:14895550
bug:14893836
bug:14893333

(cherry picked from commit e10c61bb13373b95ba857cc3af60f94b9941ab9e)

Change-Id: I083f6d5713fd55e44b7e14a9bef7ec136fac3ce4
10 files changed