LG-490 Verify password hashes without digesting salts

[jmhooper]

Why: Previously, we generated 20 char random strings for our
password salts. To get those string to an appropriate length for an
SCrypt salt, we took a SHA256 digest of the string.

We plan to start using 32 random bytes for the salt so we can use them
directly instead of hashing them. This commit adds the code to read the
new digests and tests to verify the old digests can still be verified
after the change to 32 random bytes is implemented.

This commit will not have any impact when deployed, but allows instances
generating 20 byte and 32 byte digests to serve traffic together so that
we can make the change to 32 byte digests.

Hi! Before submitting your PR for review, and/or before merging it, please
go through the following checklist:

• For DB changes, check for missing indexes, check to see if the changes
  afect other apps (such as the dashboard), make sure the DB columns in the
  various environments are properly populated, coordinate with devops, plan
  migrations in separate steps.

• For route changes, make sure GET requests don't change state or result in
  destructive behavior. GET requests should only result in information being
  read, not written.

• For encryption changes, make sure it is compatible with data that was
  encrypted with the old code.

• For secrets changes, make sure to update the S3 secrets bucket with the
  new configs in all environments.

• Do not disable Rubocop or Reek offenses unless you are absolutely sure
  they are false positives. If you're not sure how to fix the offense, please
  ask a teammate.

• When reading data, write tests for nil values, empty strings,
  and invalid formats.

• When calling redirect_to in a controller, use _url, not _path.

• When adding user data to the session, use the user_session helper
  instead of the session helper so the data does not persist beyond the user's
  session.

• When adding a new controller that requires the user to be fully
  authenticated, make sure to add before_action :confirm_two_factor_authenticated.

[jmhooper]

Having some issues w/ some test so I'm flipping to WIP

[jmhooper]

Got it green. Ready for review.

[stevegsa]

LGTM