Bug 9611: (follow-up) move new password hashing routines to separate module

Bug 9611: (follow-up) move new password hashing routines to separate module

The move avoids a problem where many modules would gain
a dependency on C4::Auth just because C4::Members needs access
to hash_password().

This patch also adds a couple unit tests for the new password
hashing code.

To test:

[1] Verify that there are no regressions on the test plan for bug
    9611.
[2] Verify that t/AuthUtils.t and t/db_dependent/Auth.t pass.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>