Problem: The POSIX functions getpwnam() and getpwuid() are not
guaranteed to be thread safe. And as the synopsis indicates, they were
being called after the server has spawned additional threads.

Solution: Write wrapper functions around the thread-safe versions
getpwnam_r() and getpwuid_r() which returns the passwd information in
an object with value semantics so that it can be safely copied,
assigned and stored.

Change-Id: I8aebe94c46f5d8be69a129dd89c40f181ad16187
(cherry picked from commit 741add8e7570834614ff8b8317d0911a9a320861)