Only return password for account session flow if the caller is signed

with system key and have get_password permission.

Bug: 30455516
Change-Id: I78484c59e4de1dff685ab91a0a8e7a756fffd9bf
(cherry picked from commit 9342e137)
(cherry picked from commit fecfd550edeca422c0d9f32a9c0abe73398a1ff1)