Refactor code related to non-privileged mounts.

This CL modifies the code to obtain the user and group ID of the user
for non-privileged mounts when the daemon starts and keep that
information in the Platform object such that other objects can simply
obtain the information when needed.

BUG=none
TEST=Ran unit tests and tested mounting/unmounting on Cr48.

Change-Id: Ib299191ff45da260d1a6de617e052131aa9e906a
Reviewed-on: http://gerrit.chromium.org/gerrit/5229
Reviewed-by: Darin Petkov <petkov@chromium.org>
Tested-by: Ben Chan <benchan@chromium.org>
10 files changed