Add user for credstore.

The credstore system daemon is running as an unprivileged user. This
CL adds this user and also creates a directory (/data/misc/credstore/)
where this daemon can store its data.

Bug: 111446262
Test: N/A
Change-Id: I8da2c32dd04fef797870b8a7bbc5e499bed71f9e
2 files changed